Librdkafka now compiles on OSX 10.9

Refactored endian support to seperate file called endian_compat.h
that will fix two implicit declaration of function errors. Also
fixed a whole bunch of use of GNU old-style field designator
extension errors
Merge pull request #51 from dvanliere/master

Librdkafka now compiles on OSX 10.9
Clarify available compression support (none, gzip, snappy)