Rsmtool

This is a major release.
1. Completely overhauled the documentation. Instead of relying on a collection of loosely organized markdown files, the documentation is much more cohesive and hosted on [readthedocs](http://rsmtool.readthedocs.io). It now includes a clear introduction to what RSMTool is as well as tutorials.
2. The RSMTool API is now richer and explicitly [documented](http://rsmtool.readthedocs.io/en/latest/api.html).
3. `rsmcompare` can now compare two `rsmeval` experiments as well as an `rsmtool` experiment to an `rsmeval` experiment.
4. Code coverage is now automatically computed as part of CI testing.
5. Expected warnings are now suppressed when running the tests.
6. Fixed several stylistic issues in the codebase raised by pep8 and pyflakes.

- Added files necessary for submission to the [Journal of Open Source Software](http://joss.theoj.org).

This is a hotfix release that fixes the following regression:
- `rsmcompare` now does not accidentally swap the old and the new experiments.

New features
- Evaluations on the test set now include R2 and RMSE.
- The `rsmtool` reports now include model fit parameters (R2 and adjusted R2) for the training set.
- It is now possible to exclude candidates with less than X responses from model training/evaluation.
- `rsmcompare` can now handle experiments which used SKLL models.
- `rsmcompare` now includes a notebook for consistency between human raters (thanks bndgyawali!)

Bug fixes
- Correct handling of repeated feature names in the feature .json file.
- Correct printing of feature coefficients for SKLL models.
- Correct handling of quoted boolean values in config .json file.
- Fixed rounding and highlighting in feature correlation table.
- And several dozen more.

This is the first GitHub release for RSMTool. Before being open-sourced, RSMTool was an internal research project at the Educational Testing Service.