Math: Rename constants & add RadToDeg() and DegToRad()

- I changed constant names to CamelCase, since I consider this visually
  more appealing.
- Removed 32-bit constants, since I don't use them (and anyway, I don't
  think that double precision constants would be a big performance hit
  anyway)
- Added radian to degree conversion functions
Disable microsoft compiler warning C4351
Common: Merge PodString with stringutils