Restructure project to enable custom mavlink bindings generation (#223)

* Restructure project to enable custom mavlink bindings generation

Split the project into three crates:

* mavlink-core: core MAVLink types including TCP, UDP and serial connections
* mavlink-bindgen: a library & CLI for generating Rust bindings for MAVLink dialects
* mavlink: generated MAVLink bindings for the MAVLink dialects in the mavlink/mavlink repo

* run GitHub checks

* reformat

* attempt to fix cross compile test

* attempt to install cross

* Downgrade clap to support MSRV 1.65.0

* Downgrade clap_lex to support MSRV 1.65.0

* Another downgrade

* downgrade anstyle

* Simplify support for MSRV 1.65.0

* Hopefully this works

* fix embedded build

* Fix build on MSRV

* Make cli feature not default

* Only build the mavlink package in tests.

The mavlink-bindgen crate does not itself need to run on embedded hardware

* Attempt to support no_std in mavlink again

* Fix for the last GitHub action

* Make the embedded example work in the cargo workspace

* Remove unused import

* Remove accidentally committed binary