adding test cases for get_features_by_ids
added test case for get_features_by_ids. Extracts study 5 from mask data and from this id arrives at 3 features. Checks shape of features.
removed mask test within test_get_features_by_ids
Merge pull request #34 from stymy/master

test case for get_features_by_ids
fixed decoder bug
Fixed random vox selection and added test
Added test for region-based averaging
updated README
Added function to classify to get order that requested features appear in dataset. Good for knowing what order data is given and rearranging
Converts ids to ints if they are incorrectly represented as strings
Removed n_jobs=-1
Removed n_jobs=-1