refactoring suggestions

* added a .gitignore; got rid of the checkpoints within the repository
* kickoff.md contains a few thoughts on how to pitch this project during the Oct 21 DoML session
* refactoring: put current data processing / ML code into a bikesharePredictor class; would like some feedback on how to organize different class methods/variables for these things
* there are lots of TODOs within the ipython notebook; let's discuss them quickly and figure out what to do next the next time we meet in person :)