Add contributor's guide

Closes #8.
semicolon
Rework Licensing stuff
Merge pull request #13 from adorableio/contributing

Contributing!
Update README.md
Allow requests with a single size
avatar swap
avatar and webserver update
adding the new dependencies to package.json
new avatars
count images in img dir
new avatar names
Improve Bucketer functionality and change namespace

* Rename Bucketer class to SlotMachine
* Pass array of things to SlotMachine and return a thing
New avatar images
redirect to avatars site on index route
adding contributors to readme
Updating the server tech