unified check_feature check_regression_feature
remove classmethods from SDMBulder, fixed docs
minor docs improvement
Merge remote-tracking branch 'upstream/master' into regression_features_check

Conflicts:
	menpo/fitmultilevel/test/sdm_test.py
Merge pull request #434 from jabooth/regression_features_check

check_regression_features unified with check_features, classmethods removed from SDM