Proposed commit log message:
```
[NEW PORT]: comms/py-xmodem: XMODEM protocol implementation
Python XMODEM protocol implementation
This is a literal implementation of XMODEM.TXT, XMODEM1K.TXT and
XMODMCRC.TXT, support for YMODEM and ZMODEM is pending. YMODEM should
be fairly easy to implement as it is a hack on top of the XMODEM
protocol using sequence bytes ``0x00`` for sending file names (and some
meta data).
WWW: https://github.com/tehmaze/xmodem
Reviewed_by: koobs
Approved by: koobs (mentor)
Differential_Revision:
```