Add some string util, work on config API

config: setting_as_int()
util: string_to_int(), string_match()
Add unit tests

Config setting fields can now have an underscore instead of just
alphanumerics.
Move PAUSE_ON_WIN32() macro to new debug.h

Also downcased it to pause_on_win32().
core/util: Fix sign issue, clean up code

"- 123" would parse as -123, despite space between minus sign and actual
number. "- 123" now properly parses as a positive integer; the negative
multiplier is set for each non-digit character parsed.
tests/core/string: Make string_to_int_test() func

Also checks for expected integer result parsed from the string, and
warns on errors as needed.
Work on IDE render subsystem

- Tweaked front_vert shader to use model, view, and projection
  transforms when calculating final vertex position.
- Add primitives objects buffer
- Add primitives scene
- Add draw buffer for all IDE rendering commands
- Add initialization subroutines where appropriate