gsmopen: continue AT control with tcblib, most of the AT timeouts are now 1/10th of sec, eg: 100millisec

Thanks to Phil Zimmermann for the code and for the license exception
we needed to include it.

There remains some build system integration work to be done before
this code will build properly in the FreeSWITCH tree.

More build system work may be needed.

Thanks to Travis Cross for much of the language here.
Signed-off-by: Philip Zimmermann <prz@mit.edu>
Signed-off-by: Travis Cross <tc@traviscross.com>

Thanks to Travis Cross for much of the language here.
Signed-off-by: Philip Zimmermann <prz@mit.edu>
Signed-off-by: Travis Cross <tc@traviscross.com>

(refs #25)

(refs #24)

(refs #25)

(closes #26)

(closes #23)

(closes #22)

ZRTP_SRTP_HASH_SHA1 was moved from public zrtp_hash_id_t to the
private srtp implementation. HMAC SHA1 constant was also renamed to
ZRTP_SRTP_HASH_HMAC_SHA1 in order to raise an error if the user tries
to use an old ZRTP_SRTP_HASH_SHA1 constant in a ZRTP session
configuration.