Create the stub for a brush feature.
Adding the basic brush feature.
Additional work on the brush feature.
Merge branch 'master' into brushes

Conflicts:
	d4.js
	test/lib/d4.js
Add a failing test for the rangePoint bug.
This commit fixes issue #18
remove console statements.
Adding additional code to round out the brush feature, which helps determine how
to calculate if a selected object is within the brush's extent. Additionally, I
added two helper methods isNull and isNotNull to d4.base.
Update the brushing code to use the d4 accessor pattern.