Use zlib for BGF resources

Introduces BGF version 10 based on zlib compressed pixeldata instead of crusher.
Adds implementations to writebgf.c (compression) and dibutil.c (decompression)

The dibutil.c part has been successfully tested.
It supports both, version 9 (crusher) and version 10 (zlib)

The writebgf.c is untested and by default should now write version 10 instead of 9.

See the request/issue tracker:
https://github.com/Meridian59/Meridian59/issues/32

Example BGF compressed with zlib (ivy circlet):
https://googledrive.com/host/0B-6rsj6uHlolV2ZGMjNQLUZiLXc/ivycircl.bgf