Merged in syrja/speedcrunch/gradian (pull request #95)
Added conversion functions between radiand and gons.
Added gradians to user intreface (minus shortcut).
Corrected gradians() function.
Add gon unit.
Added tests for new angle units.
Added conversion functions between radiand and gons.
Added gradians to user intreface (minus shortcut).
Corrected gradians() function.
Add gon unit.
Added tests for new angle units.