Add Sign Function, Define ceil, floor, pi

Adds sign function sgn(n) that returns -1, 0, or 1 depending on sign of
n. Defines math.ceil, math.floor, and math.pi as ceil(), floor(), and
pi(), respectively.
revised stupidity

added sgn() to lib, removed ceil, floor, pi because I put them in the
wrong place in the first place and didnt realize they were already where
they should be
Merge pull request #31 from suchipi/master

Add Sign Function, Define ceil, floor, pi