Framework core platform independence

- Removed absolute need for love.filesystem (but it's still used if it's
available)
- Added the "platform," "platform_version," and "framework_version"
fields
- Cleaned up body code very slightly
Upgraded to Windows 8.1 on my primary dev machine
Make small filesystem library wrapper

This is something with the intent to simplify libraries that can run on
multiple platforms, so far including LÖVE and regular Lua. Possible
future targets include Corona, the TI-Nspire SDK (doubtful) and others.
Add utility.math with a single method

Right now, this math library isn't very useful because of Lua's
exclusive use of doubles for all numbers.
Rewrite utility.version FS calls