Merge pull request mottosso#25 from monkeez/api-units

* UiUnits for distance and angle, DGContext uses seconds by default

* Added unit argument to DGContext

* Added UiUnit alias

Merge pull request mottosso#16 from mottosso/usability

Usability

Merge pull request mottosso#14 from monkeez/dgcontext

Added DGContext class

Merge pull request mottosso#11 from mottosso/convenience_aliases

Add convenience aliases for common types and attributes

Merge pull request mottosso#9 from mottosso/set_matrixplug

Add support for writing to a matrix plug

Merge pull request mottosso#8 from mottosso/python3_metaclass

Improved Python 3 support

Repair setup.py