Work on datac4, datac5, datac13, selective repeat ARQ

[DJ2LS]

This PR contains work on implementation of datac4, datca5 and datac13.

For usage, latest code from codec2 dr-datac4 is needed.

This PR causes a minor incompatibility with older versions!

• datac13: new signalling mode, 68 bit/s payload, -10dB AWGN, -4dB MPP, 3 carriers
• datac4: new low snr mode, 87 bit/s payload, -8dB AWGN, -4dB MPP, 4 carriers
• datac5: new high speed mode, 1700 bits/s payload, 7dB MPP, 2200 Hz - not yet implemented

Todo:

• Implement modes to modem module
• Increase ARQ protocol version
• Check timing for ARQ protocol
• Remove datac0 code
• Optimize codec2 module where possible
• Optimize modem module where possible
• adjust ctests
• make code ready for selective repeat ARQ

Before merging to main: check for correct codec2 branch