add mermaid diagram to libusb wrapper docs

src/pc/protocols/wrap_libusb.md

@@ -13,7 +13,7 @@ from this base resource type.
 
 `dp::libusb` is currently focused on the needs of XLink; the protocol to communicate with
 Intel Movidius/Myriad devices. A `std::shared_ptr` base for resources was considered for
-some use cases. It was not implemented due to the limited needs of XLink.
+some use cases. It is not implemented due to the limited needs of XLink; a single owner.
 
 Many raw libusb types, e.g. `libusb_device_descriptor`, are used in their simple POD form.
 Some libusb resources are not implemented, e.g. asynchronous device I/O.
@@ -34,13 +34,121 @@ Most behaviors of `dp::libusb` resources derive from `std::unique_ptr`.
    with error text sourced from `libusb_strerror()`.
 6. Raw resource pointers can be retrieved with `get()` to use with libusb C apis.
 
-## Types Overview and Hierarchy
+## Object Model and Types
 
-mermaid tbd
+All libusb wrapper classes are derived from `unique_resource_ptr<libusb_****, disposeFunc>`
+where `libusb_****` is the native libusb POD struct and `disposeFunc` is the native libusb disposing function.
+
+`unique_resource_ptr<>` is a helper class that inherits from `std::unique_ptr<libusb_****, unique_resource_deleter<libusb_****, disposeFunc>>`. It uses the normal `std::unique_ptr` custom deleter feature to automatically call `*disposeFunc(unique_ptr::get())`.
 
 * `usb_context` enhances raw `libusb_context*`
-* `device_list` container exposes iterators to raw `libusb_device*`
+* `device_list` stl container generates and grants access to all `usb_device` on the host
 * `usb_device` enhances raw `libusb_device*`
 * `device_handle` enhances raw `libusb_device_handle*`
 * `config_descriptor` enhances raw `libusb_config_descriptor*`
-* remaining libusb types are used unchanged
+* all remaining libusb classes and structs are used unchanged
+
+The typical process is
+
+1. Create a `usb_context`
+2. From that context get a `device_list`
+3. From that list choose a `usb_device`
+4. From that device get a `device_handle`
+5. Operate and transfer on that handle
+6. All resource lifetimes are RAII managed including resource release/free/exiting.
+
+### Class diagram
+
+In this diagram, the inheritance `public unique_resource_ptr<libusb_****, disposeFunc>` is abbreviated `resource<libusb_****, libusb_disposeFunction>`.
+
+[Click to use Mermaid Live](https://mermaid.live/edit#pako:eNq1V1uP2kYU_iuWI0WADAvGMZdIedimVfPQviRPCZE12Md4tPaMOzMmkC389p6xjT027GZTtTywzDnfd-5z2Uc75BHYaztMiZTvKdkJkm1YRAWEinJmfbrfsA2z8FPIbRBypuCgrPH4nRXBnoYQpFSqCmAISoAmVLLWQLU2-QlhUXobgd5iukOJDAXNFRcVqvouA-4E9Vgp9EeA5IUI4ZzSrQF55XlvX83dt7UUDlSdK9LpkmVl1kzFMCtVqunaGqEMhF7wWH_3c-3VY2AEMbRq9ztQgYkZttRzR34hxALgKQbPQRAs0ZeviL8VzRZ2lHV0AVUVx0iQfgfTqlTYHSKioEk5yEAlPJIBKhoDcjKZXGi9ShotfaY_FaLXnoIJiGvVueW2-EGHPWrq1NIGuRLdIukSdCbvYqTUYUsGw6HB0D26GsNBJfnAIjj0sLVpA9sDoK-AFdkWrjQ5F6pWySeK2Qn8x_Wsgb2yhimXZj271WjZTTmrqj1HqCfbseRRvof976Wm4X8TJA9Qc-nJzZINbmyLuh0tHKtAs4CiMxET1De__izLNjQLkgKR8CJs2-MCpxkPvc4OuFJ2Vh-Y6lmSSlBmTktAZEjpoBX050a7IIXiyFEkTIIHEAzSIBJ0j1Oy5TztgTNyCHISPmhvesMCi3KO-Tnl_u3F8xT4ZwZ3W6QPgRKEyRgjat2NtkWMEseq_n7sen-K1Zwl9yXr3_lB4QUoIHIsRTPghZmVdiN42toT8FcBUn065siuF461J2mBa6qb8oSna9vlMIkiV_9JtL1dfnXe_OBm64J7u728M65A506ZeqdbewQ4lnnSmRv0mtXP5ZJvgCljCuPx39WLoFy2172hxSNCQdYBMIpdCi45B3ia14YqBa7NJwEjGUicdbASSPE-lLpwZmVND9aXjS1VtF533NpfL8W-cY9VvMfuVVQKB-X3L_iUGj6rdaxvCVE_gelF0SuqEUpXY1ozBu_-qEAOX0LSIfwf1H5Vmz427WhFr1N1meLRaORYEZU5Xl2_FSx8ZzSqfC-1LLxIQpKm0hoZ-M5NcjuGzpBhMDfELwyosX-yHTsDkREa4Qu71G5slUAGG3uNPyOISZGqjb1hGqrvgI9HFtprJfBIsos8IgrqN3lX-GtEcc_Z65ikEoUpJxHg8tFWeLihrx2-DtFitUu1vBApihOlcrm-u9PqyY6qpNhOQp7dSRolRKhkv_LvfNdfEncO_mJO3sznUbidrZax683iaDGducQ-nRw7J0xbPdjrsed6E89feSt_OvP82dJ17COKV-5ksZj6b1bucjGfrvwlsr5zjnnMED6bekvXnS7n_nI29xwbynz-qP8V0X9KH59LQpnk6R86Wkid) if you can not see the chart below.
+
+```mermaid
+classDiagram
+direction TB
+
+    usb_context --> device_list
+    device_list --> usb_device
+    usb_device --> device_handle
+    usb_device --> config_descriptor
+    
+    class usb_context {
+        resource~libusb_context#44;#32;libusb_exit~
+    }
+
+    class device_list {
+        stl#32;container#32;of#32;usb_device
+        device_list(usb_context) libusb_get_device_list()
+        ~device_list() libusb_free_device_list()
+        operator[]() usb_device
+        begin() usb_device_iterator
+        size()
+        standard_container_methods_and_iterators...()
+    }
+
+    class usb_device {
+        resource~libusb_device#44;#32;libusb_unref_device~
+        usb_device(libusb_device*) libusb_ref_device(ptr)
+        open() device_handle(libusb_open(get()))
+        get_config_descriptor(configIndex)
+        get_device_descriptor()
+        get_bus_number()
+        get_port_numbers()
+    }
+
+    class device_handle {
+        resource~libusb_device_handle#44;#32;libusb_close~
+        device_handle(usb_device) libusb_open()
+        device_handle(usb_context, sysDevHandle) libusb_wrap_sys_device()
+        get_device() libusb_get_device(get())
+        claim_interface(interfaceNumber)
+        release_interface(interfaceNumber)
+        get_configuration()
+        set_configuration(configurationInt)
+        get_string_descriptor_ascii(descriptorIndex)
+        set_auto_detach_kernel_driver(bool)
+        set_max_packet_size(endpoint, size)
+        get_max_packet_size(endpoint)
+        get_device_descriptor()
+        bulk_transfer(endpoint, *buffer, bufferSize)
+        bulk_transfer(endpoint, containerBuffer)
+        bulk_transfer(endpoint, *buffer, bufferSize, *transferred, timeout)
+        control_transfer(requestType, request, value, index, *buffer, bufferSize, timeout)
+        interrupt_transfer(endpoint, *buffer, bufferSize, *transferred, timeout)
+    }
+
+    class config_descriptor {
+        resource~libusb_config_descriptor#44;#32;libusb_free_config_descriptor~
+        config_descriptor(usb_device, configIndex) libusb_get_config_descriptor()
+    }
+
+    transfer_error --|> usb_error
+    usb_error --|> system_error
+    unique_resource_ptr --|> unique_ptr
+    
+    namespace helpers {
+
+    class system_error ["std::system_error"] {
+    }
+
+    class usb_error {
+        usb_error(errorCode)
+        usb_error(errorCode, what)
+        usb_error(errorCode, what)
+    }
+
+    class transfer_error {
+        transfer_error(errorCode, transferredBytes)
+        transfer_error(errorCode, what, transferredBytes)
+        transfer_error(errorCode, what, transferredBytes)
+    }
+
+    class unique_ptr ["std::unique_ptr&lt;libusb_***, disposeFunc>"] {
+        ~unique_ptr() calls *disposeFunc(get())
+    }
+
+    class unique_resource_ptr ["unique_resource_ptr&lt;libusb_***, disposeFunc>"] {
+    }
+
+    }
+```