OSX Support for crown

Will add individual comments in source files.

I'm not even close to 100% confident in the changes I've made in genie / the makefile. I'm having trouble getting bgfx to compile right now : https://github.com/bkaradzic/bgfx/issues/211 but once that's straightened out I can resume testing.

I was having trouble getting luajit linked correctly initially so I just ended up linking to my usr/local/lib folder. I removed that crap before I created the pr, but I haven't tested linking against the included luajit directory yet, so please excuse me if there are a bunch of linker errors.

Anywho, all the source changes, if everything is linked correctly, should result in a mostly functioning crown engine. I think there is still some more stuff to hook up with the native window - not sure I got all the window events hooked up, but it's mostly there. It's a starting point at the very least.

I had to change the name of assert.h - I picked ceassert.h. Another header file which was being link pulled in the stdlib assert.h. Not sure how exactly you want to handle that, but if you need me to get specifics on which header was causing the problem I can.

Again most changes should have comments by them explaining why I made them.
https://github.com/taylor001/crown/blob/64d093e60875ff0756dd5c77dcb23af03a8eab85/genie/toolchain.lua#L168
Should be PHYSX_SDK_OSX/Lib/osx64, I guess?