* Draft combined gather/score method
* Remove gather_and_score function, as it was much slower than the separate processes.
* Ignore features if they are all zero valued
* Improve const correctness in learner.pyx
* Improve const correctness of weights.pyx
* Improve const correctness for count_feats
* Short-circuit the map array idea, always using the first element of the array.
* Use n_templ in the feature hash, short-circuiting the idea of having a map array
* Fix Cython division directives
* Update to use the new preshed version, which supports iteration and zero keys
* Switch from PreshMapArray to PreshMap
* Tweak model writing, removing extraneous total_freq
* Work on getting travis-ci to work