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 esp-rs/esp-idf-sys#7 (comment).
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

• Decouple library from platformio and refactor code.
  • Separate all code that is general purpose.
  • Rename things that reference pio.
  • Test code and update readme
• Implement some CLI argument utilities
  • Parsing a windows/unix command line into a Vec of arguments.
  • Querying arguments.
  • Implement correct handling of arguments (in ldproxy, etc.).
• Changes for esp-idf-sys cmake build #14
• Use reponse file on windows and when using gcc #15
• Add documentation
  Not everything has been documented but this should be enough for now.