Feature/req vars

[abea]

Resolves #25

• Adds plugin to check for variable use
• Sets properties that will require variables, including all colors via regex
• Sets certain keywords allowed instead of variables
• Updates README to include plugin installation instructions

[abea]

Should we do this to a new develop branch to work on proper versioning?

[austinstarin]

@abea Looks good. Thanks for taking the lead on this.

That would be great. You need to bump the version in package.json every time you commit to master so that we can publish on npm.

[abea]

Changed to merge into dev branch.