Noise Update/Terrain Generation Test

Factored FMA (fused multiply-add) support into its own file, so the
compiler can automatically switch between regular multiply followed by
add and FMA depending on whether there's a "fast" (i.e. hardware)
implementation available (FMA on CPUs without hardware support was
lagging terrain generation by 10-33%).

Added FMA in a few more places.

simplex.hpp and simplex.cpp have been renamed to noise.hpp and noise.cpp
to more accurately reflect their purpose.

Removed the old world management code -- it needs a rewrite.

Updated random.hpp to be generator-agnostic.

Started prototyping terrain generation using the simplex_test programs
combined with an updated PHP GD script.