move all sources into a cargo workspace (#1)

this step just moves everything out of `sources/` and
places it into `crates/`. `cargo check` passes after
adding making the crates workspace members in the root
`Cargo.toml`.

The crates do not refer to each other by path, and they
are also not yet cleaned up.

.gitignore

@@ -0,0 +1 @@
+target/