Release 0.19.0

+  Added support for running ablation experiments with *all* combinations of
   features (instead of just holding out one feature at a time) via
   ``run_experiment --ablation_all``. As a result, we've also changed the
   names of the ``ablated_feature`` column in result summary files to
   ``ablated_features``.
+  Added ARFF and CSV file support across the board. As a result, all
   instances of the parameter ``tsv_label`` have now been replaced with
   ``label_col``.
+  Fixed issue #71.
+  Fixed process leak that was causing sporadic issues.
+  Removed ``arff_to_megam``, ``csv_to_megam``, ``megan_to_arff``, and
   ``megam_to_csv`` because they are all superseded by ARFF and CSV support
   in ``skll_convert``.
+  Switched to using Anaconda for installing Atlas.
+  Switched back to `skll.readthedocs.org <http://skll.readthedocs.org>`__
   URLs for documentation, now that rtfd/readthedocs.org#456 has been fixed.