Renamed DXF::Builder to DXF::Unparser
Added testing for Sketches with groups and transformations
Require units v2.2

Units::Literal was renamed to Units::Numeric
Small fixes
Implemented basic file parsing

This has a long ways to go, but the at least the infrastructure is there. From here it shouldn't be too hard to add support for the missing elements as needed.
The units gem's repository was renamed