Support Hunspell personal dictionary and Git repository syncing

Summary:
A Git repository will allow easy backup and sync across machines.

The Hunspell format can be used by Atom, Nano, Vim, etc.

Improve documentation and refactor application to better support
several formats.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2604