improve size related traits

- rename `Size` trait to `DataSize`.
  - new associated consts `BITS`, `BYTES`, `UBYTES`, `UBITS`.
  - remove unnecessary methods.
- new generic traits: `Bitsize`, `BitSizeAtLeast`, `BitSizeAtMost`.
- implement on most of the Rust primitives.
- improve docs and refactor the `mem` module.

src/lib.rs

@@ -33,5 +33,5 @@ pub mod unit;
 /// Everything is re-exported from here.
 pub mod all {
     #[doc(inline)]
-    pub use super::{error::*, grid::*, list::all::*, mem::*, misc::*, unit::all::*};
+    pub use super::{error::*, grid::*, list::all::*, mem::all::*, misc::*, unit::all::*};
 }

src/list/mod.rs

@@ -13,5 +13,5 @@ pub mod stack;
 pub use all::*;
 pub(crate) mod all {
     #[doc(inline)]
-    pub use super::{bit_array::all::*, array::all::*, deque::*, linked::*, queue::*, stack::*};
+    pub use super::{array::all::*, bit_array::all::*, deque::*, linked::*, queue::*, stack::*};
 }