Repository for new the Osmocom BTS implementation.

This code implementes the Layer 2 and higher of a more or less
conventional GSM BTS (Base Transceiver Station) - however, using an
Abis/IP interface, rather than the old-fashioned E1/T1.

Specificallt, this includes
 * BTS-Side implementation of TS 08.58 (RSL) and TS 12.21 (OML)
 * BTS-Side implementation of LAPDm (using libosmocore/libosmogsm)
 * A somewhat separated interface between those higher layer parts
   and the Layer1 interface.

Right now, only one hardware and Layer1 are supported:  The sysmocom
sysmoBTS.

There is some experimental and way incomplete code to use a couple of
OsmocomBB phones and run them in the BTS.  However, the required code
for the Calypso DSP code have not been written yet.  This would still
require a lot of work.

Some additional work is being done in using some parts of the OpenBTS
L1FEC and glue it against omso-bts.  However, this is also still in an
early, experimental stage.