Reimplemented sin, cos, and tan for non-empty intervals.
Layout.
Merged reimplementation of inverse trig functions, without merging the doctests that were concurrently developed.
Improved documentation of periodic function.
Improved handling of trig functions on intervals that exactly begin at a local extreme.
Improved documentation.
Merge fix for edge case in trig functions.
Added test case for edge condition that had previously failed.