Add an os x output

[rbouqueau]

https://github.com/tpoechtrager/osxcross

[rbouqueau]

This one was tested on another project: https://github.com/Tatsh/xchain

[rbouqueau]

OSX builds already since #21

For the toolchain, see http://docs.travis-ci.com/user/languages/objective-c/

[rbouqueau]

Ok they rely on HomeBrew... CC @RodolpheFouquet

[rbouqueau]

And so basically it doesn't work. Reverting... 602db34