Hyperbolic functions.
Merge pull request #9 from eggrobin/elementary-functions

Elementary functions
Don't reinvent the wheel.
Merge branch 'quantities-tests' of https://github.com/eggrobin/Principia into quantities-tests
Tested trigonometric functions.
Dimensionful ArcTan
Test all the things!
Test more of the things!
Merge pull request #10 from eggrobin/quantities-tests

Quantities tests