c2gmsk: API version 20130606: auxiliary data service + migration to LGPL

[Kristoff Bonne]

Hi All,


I have just commited API version 20130606 to github.

1/ As discussed before, new in this release (compaired to 20130601) is
the "auxiliary data service" in the 2400 bps modem.

The procedure works like this:
* on the sending side:
-> the API call "c2gmsk_auxdata_sendmessage" will queue a message to be
send by the modem.
The text will be send at the rate of 100 bps, or 1 nibble (= 4 bits) per
audio-frames of 40 ms. The end of the message is marked by a "null"
marker (i.e. a character containing 0x00).
-> when the text has been completely send, a message
"C2GMSK_MSG_AUXDATA_DONE" is returned by the API to the modulator when
the frame containing the last nibble of the terminating null-char has
been send
-> when no data needs to be send, the "null" character is send


* on the receiving side:
When a stream it being received, a message "C2GMSK_MSG_AUXDATA" is send
to the API to the application when a complete message has received (i.e.
when the terminating null-char has been received).


2/ I've also taken the opportunity to change the license on the code
from GPL to LGPL.

Of course, I have only changed the license of the code written by
myself. Most other code was already under the LGPL license by their
respective authors. Only the low-level GMSK DSP-filters are licensed
under GPL by the author.



The 2400 bps modem still carries the version-id 2400/15 (15 =
"experimental") as I am still waiting for additional test-results.

73
kristoff - ON1ARF