gsm

Here is a branch that drops the internal gsm
and only supports gsm as an external format.
https://sourceforge.net/u/janstary/sox/ci/gsm/tree/

I also propose to drop the support for an external gsm altogether.
The format is supported by libsndfile, which is actively maintained,
as opposed to gsm implementations out there.

And I also propose to drop the internal lpc in the same way;
in fact, to drop LPC support altogether. Is anyone using it?

Then we would finally have no SUBDIRS.

	Jan