Add new labels (Documentation/Testing)

[mdvsh]

I'm currently contributing an automatic PR labeler to this package as part of my task in Google Code In.

I believe that by adding "documentation" (for detecting change in a markdown file) and "Testing" (detecting a change in the /test folder) labels, the package contributing can be made much easier.

Regards,
PseudoCodeNerd

[logankilpatrick]

Will also need a "CI" label.