support for various angular units in std.math

[KB]

For a very tidy and typesafe implementation of units I would recommend checking
out the units feature in F#.

http://blogs.msdn.com/b/andrewkennedy/archive/2008/08/29/units-of-measure-in-f-part-one-introducing-units.aspx

Probably not the best link, but the compiler will flag if units are not consistent
in computations.

Also accept they adopt a 'tagging' system to declare units, but conversely it is
very extensable to any set of defined units.

K