Add handling for non-unicode return values from datetime.strftime

Hopefully fixes #3.
Update README to use relative links where applicable
Code overhauls (no changes in functionality)
Add generate_table.py which I've only been using locally
Add ability to modify default settings
Add .sublime-commands file with default and custom format

Closes #1.
Add a few key bindings
Add key bindings to menu file
Update README and install.txt (now .md) and create CHANGELOG
Finish v0.4.0