change license to MPL 2.0

To prepare gen_zmq to become a zeromq community project and
make it compatible with with C4.1 [http://rfc.zeromq.org/spec:22],
change license to MPL 2.0.

Signed-off-by: Andreas Schultz <as@travelping.com>
fix indention in all files

automated cleanup: use 4 spaces indention consistently
and replace all tabs with 8 spaces