Tracking issue for making the library build system agnostic (`embuild`).

[N3xed]

This is the tracking issue to create a more build system agnostic library.

This is done to support building the esp-idf natively (without platformio), see https://github.com/esp-rs/esp-idf-sys/pull/7#issuecomment-899035142. As it will not be build system specific anymore, the library and the cargo-pio-link tool will be renamed:

• The library will be renamed to embuild.
• cargo-pio-link will be renamed to ldproxy.

Steps

• [x] Decouple library from platformio and refactor code.
  • [x] Separate all code that is general purpose.
  • [x] Rename things that reference pio.
  • [x] Test code and update readme
• [x] Implement some CLI argument utilities
  • [x] Parsing a windows/unix command line into a Vec of arguments.
  • [x] Querying arguments.
  • [x] Implement correct handling of arguments (in ldproxy, etc.).
• [x] #14
• [x] #15
• [x] Add documentation Not everything has been documented but this should be enough for now.