Document project status in README.md and lib.rs

This commit adds quite a bit of documentation about the current status
of the project, including links to GitHub issues for the different Rust
modules which map to specific pieces of functionality.

The intent is to track the current status of the project in the
README.md as that's more up-to-date than the docs.rs documentation
(which depends on a crate release to get updated).

src/apdu.rs

@@ -39,8 +39,7 @@ const APDU_DATA_MAX: usize = 0xFF;
 
 /// Application Protocol Data Unit (APDU).
 ///
-/// These messages are packets used to communicate with the YubiKey using the
-/// Chip Card Interface Device (CCID) protocol.
+/// These messages are packets used to communicate with the YubiKey.
 #[derive(Clone)]
 pub(crate) struct APDU {
     /// Instruction class: indicates the type of command (e.g. inter-industry or proprietary)