Implemented exporting of nested Sketches
Everything needs to have a layer

AutoCAD appears to be rather picky about that
Tell bundler to get the sketch gem from GitHub
Configured for Travis-CI
Tell bundler to get the units gem from GitHub
Added a direct dependency on the geometry gem

It was previously being required indirectly via the sketch gem. The dependency should be direct because the dxf gem uses geometry objects and methods directly.
Require sketch v0.1
Added Travis-CI status image to README
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
Renamed the repository to dxf-ruby

To be consistent with my other ruby gems
Improved checking for values with units in Unparser

Check that the value actually has units before attempting a conversion. This was exposing a bug in the units gem that caused a crash when trying to convert a value without units. Even with that bug fixed, this would have caused undesired conversions because unit-less numbers shouldn't be converted on output.

Also, rely on duck-typing instead of checking for a particular class.
Implemented output of lightweight polylines

Polyline, Polygon, Rectangle and Square now generate LWPOLYLINE instead of a pile of LINEs.
Updated the copyright notice
Added support for Units operator proxies
A small fix for handling PointZero

Calling map on an infinite sequence is a Bad Thing