On ChromeOS Linux apps can't access serial port but they can connect to TCP,
so I wrote a simple app to forward TCP to serial. I suppose this can
have other uses as well.
* move communication related code from proxmark3.c and cmdmain.c to new file comms.c
* replace byte_t by uint8_t in uart_posix.c and uart_win32.c
* move OpenProxmark() and CloseProxmark() from flasher.c to flash.c
* move print_lock mutex including initializer to ui.c
* minor changes in printing help texts
* no changes in comms functionality yet
* uart: Major cleanups
- Adds documentation to the uart API.
- Fixes a buffer overflow issue in `uart_receive`, where the maximum parameter was ignored.
- Splits the maximum length and bytes recieved variables in `uart_receive`.
- Downsizes the receive buffer to the minimum required, saving 16MiB of RAM at runtime.
- Refactors the POSIX and Win32 implementations of uart into separate files.
- Removes the unused `uart_{get,set}_parity` functions, which were not implemented on Win32.
