New build system: SCons

Similar to TPT's scons, but with a lot of things fixed, including conf at the start working much better, some autodetection stuff, strip, and static compiling for windows. All options should work together, except --opengl isn't very tested.

This SConscript supports --msvc, and --universal for mac. It also has some extra options like --output and --native.

Also, mac compiling errors fixed (tested using cross compiler), renderer fixed, msvc compile fixed, and no lua compile fixed.
Fix STKM respawning when going through portals, fix SPNG dragging