added some basic trig functions

[kellender]

For issue #180
sin, cos, tan, csc, sec, cot

[aaaaalbert]

• Needs unit tests for checking proper functionality.
• Needs unit tests for checking proper exception handling.
• Should take parameters in radians, and not convert internally.
• When in doubt (e.g. on parameters in radians or exception handling), check with Python's math module.
• Should provide functions to convert degrees from/into radians, and probably something to wrap the argument back into +-pi as well.
• How commonly used are the 1/sin, 1/cos, 1/tan things? First time I see them defined with own names (but this might be an intercontinental issue.)
• Pull out the number of decimals places into a CONSTANT, or leave out altogether.
• Should probably wrap the parameter into +-pi before proceeding.

[aaaaalbert]

Re cosecans et al.: Python's math doesn't seem to have them.

Feature requests:

• Arcus functions
• Hyperbolic functions
• Area functions

[JustinCappos]

This was needed for the SAS hack-a-thon. Let's fix and merge...