Merge pull request #8 from beets/master

Feature extractors for budget and release dates
Scikit learn runner
Merge pull request #9 from maxwxzheng/master

Scikit learn runner
Merge pull request #10 from beets/master

Add feature combinators
Add the code to drop uncommon features
Fix bug in budget_bucketized and turn on caching.

Also add a tool to analyze generated features for proposal.
Merge pull request #11 from maxwxzheng/master

Add the code to drop uncommon features
Merge remote-tracking branch 'upstream/master'
Budget feature by year

The feature value is difference of budget from average budget for the
year.