make axis title and tick labels ‘interactive’ so they can receive mouse events.
add flatten to Makefile closes #73
Use y axis and group: width
Merge pull request #75 from hadley/example/barley

Improve barley example
Clean up updated barley example.
Merge pull request #71 from malecki/upstream

make axis title and tick labels ‘interactive’
Merge branch 'master' of https://github.com/malecki/vega