Feature/refactor

Added docs and renamed variables for clarity. Modules now make use of RenderResult. Changes to the player allow for multiple renderers and export options. The config file now requires a list of Renderers and a list of exporters rather than just a list of handlers.
This will fail if the file is not in the same directory as the current working directory, though I understand why you made this change. Newer versions of pydocx require you to pass a string path instead of a filepointer. This is a major limitation for the MFR. Given a filepointer, there is no way to derive it's full path. 

I've posted an issue (https://github.com/CenterForOpenScience/pydocx/issues/95). For now, I think our best bet is for mfr_docx to depend on an old version of pydocx (0.3.14) that allows for filepointers to be passed to `Docx2Html`.