Forward Error Correction (FEC) / Unconnected Protocol Support

[cbs228]

We should add a FecSocket for ARDOP's unconnected, forward error-correction mode of operation. FEC is very similar to UDP, except that packets may be repeated. FEC frames may also be co-mingled with ID frames.

The biggest hurdle is the need to specify the FECMODE. The available modulation modes change with every major release of ARDOP. We can either:

1. Tie our public API to ARDOP major versions; OR
2. Abstract the mode selection process out somewhat.

In general, (1) is the choice with the simpler implementation, and it is probably the correct one.