Add mathematical functions

[vrugtehagel]

It'd be nice to support the newer mathematical functions. Specifically:

• round()
• mod()
• rem()
• sin()
• cos()
• tan()
• asin()
• acos()
• atan()
• atan2()
• pow()
• sqrt()
• hypot()
• log()
• exp()
• abs()
• sign()

See the section on Math functions on MDN.