UHF Ground Station Code V1.0a (Si 4463 Rev. C2)

Forked off Zak's code. Most things are implemented, will have to write a shell program that is compatible with SPACE-HAUC compatible packet structure.

Zak's code was changed so that the radio does not fall back to IDLE mode after a FIFO read and thus allow RX to continue (by adding setState(SI446X_STATE_RX)).

Changelog:

1. Implemented dual serial for data and debug.
2. Implemented IRQ-driven pipe mode enable signal.
3. Implemented byte-by-byte transmission mirroring Endurosat Pipe Mode setting.

TODO:

1. Implement packet structure. (Done)
2. Test TX to Endurosat. (Done)
3. Test RX from Endurosat. (Done)
4. Confirm (and implement if necessary) AES-256 encryption and decryption protocols.
5. Implement shell mode if possible.

Info:

1. sudo modprobe nf_conntrack_pptp

2. sudo pppd -detach -crtscts noauth lock proxyarp/defaultroute <local>:<remote> /dev/tty* <baud>