Added new RNG which uses SFMT.
Move RNG exponent definition to main CMakeLists.
Replaced rand() calls with new RNG in gemrb core.
Fixed upper bound in RNG default value.
Added additional bound checks to RNG.
Replaced exception by error() in RNG.
Use previous behaviour of time assignment again.
Removed unneeded header.
Handle special cases for negative numbers, updated comments.
Merge pull request #17 from VanNostrand/rng

slightly fairer RNG