A million little clean up things
Remove support for short names for some learners.
Remove ExamplesTuple
Remove run_ablation
Change all references to classes to labels
Merge branch 'master' into feature/remove_deprecated

Conflicts:
	skll/utilities/filter_megam.py
	skll/utilities/join_megam.py
	tests/test_utilities.py
Add slicing/indexing to FeatureSet class

Also clean up a few docstrings in it.
Add FeatureSetWriter.for_path and remove write_feature_file
Fix accidental switch from property to attribute in learner.py
PEP8 fixes
Fix num_classes instead of num_labels in test_utilities
Fixed bug where `labels` conflicted with existing variables with the same name
Rename remaining instances of `classes` to `labels`
Clean up generated config files for custom learners

- added `tearDown()` method to remove automatically generated config files.
Merge pull request #199 from EducationalTestingService/feature/remove_deprecated

Remove deprecated functions and rename classes to labels