Sketch::DSL was including the wrong builder

Probably need to check this for the other builders as well
Gave the Polyline DSL a relative move command

The previous move command was moved to the Turtle DSL, but it makes sense for the regular DSL to have a relative move command that can do more than one axis at a time.
Added support for attributes
Small cleanup
Added a 'repeat' command to Polyline DSL

Repeats the geometry generated by a Turtle block along a line. The line can be specified as a step/count pair, as a destination point and step length, or as a destination point and step count.
Added methods for forcing a Sketch into the first quadrant

This is useful when exporting to a drawing
Added first? and last? to the repeat DSL

For indicating to the DSL block the first and last repetitions
Moved more methods from Sketch::Builder to the DSL module

Because it's where they belong. The group and polyline commands rely on the Builder to implement build_group and build_polyline. This makes it easier for various Builder's to override the default behavior.
Added #empty?

It does what you think it does
Moved all geometry creation to the DSL module
Refactored the Layout handling in the DSL module

There's a lot more to be done here, but this works well enough for now.
Changed the Sketch initializer to accept Transformation options

This feels unclean; a Sketch shouldn't have a Transformation. I'm not sure how else to allow for sub-Sketches with transformations.
Updated the Sketch initializer to accept attributes

This necessitated some changes to Layout to prevent it from passing its own attributes to super
Changed Layout's initializer to take *args

Having a single regular parameter was making a mess of things. This gem really needs to switch over to named parameters, but that would require ruby 2.0. I'm not yet sure if that's a good idea.
Added shortcuts for horizontal and vertical layouts

No new functionality, only syntactic sugar.
Use the new Geometry::Square class-cluster

Requires geometry v6.2 or later
Small optimizations for the Repeat builder