Support for building on osx

[medcelerate]

Would it be possible to add support for loading the ndi lib in osx?

[Julusian]

I don't expect this to be hard to do, but I don't have easy access to a mac to be able to work on this myself.

A word of warning on this library, I stopped on the project I started this for (hence no changes since May). It should mostly work fine though, but might take a little work to expand coverage to the bits of the api you need.