Made library for ring buffer mapped to a file.

Storing head/tail info at the end of the file too.
Started writing code for Bluetooth I/O.

Now uses `pthreads`.
Tried to make `ring_buf` a little thread safe.
Fixed filter setting bug in ISOBUS module.
Added filtering test/example to `sc_mod_test.c`.
Filtering works now, threading was changed.

Also changes thread stuff:
* Shouldn't lose commands anymore
* Should prevent only 1 of in/out thread dying
Merge branch 'master' of github.com:ISOBlue/isoblue-software