Remove Obj-C entrypoint.
Add Obj-C++ files to premake files.
Add autorelease.hh/mm

Only really useful on Apple platforms, otherwise they're NOPs. If the
app is compiled with ARC enable, the functions are NOPs, though the
macros will create autoreleasepool blocks. Not yet sure how well that'll
work since that would create an inconsistency between ObjC++ and C++
sources, since I'm pretty sure I can't just drop an ARC block into C++
source.

We'll see. Might just mandate that ARC be turned off permanently since
it's mostly useless here.
Add autorelease pools around logic and main threads.

This should fix the usual output at the end of the process about objects
being autoreleased without an autorelease pool.
Remove unused get_headers function from premake4.lua
Fix key callback for latest GLFW 3.

Scancode is ignored for now. Not sure if it'll be used.
Change console key to Shift+Grave.

Lot more convenient than pressing F12.