Adds some testing

[himynameisdave]

Jest testing and final cleanup before 0.9.0 goes out

Closes #30 (finally)

• [x] adds eslint, removes jshint
• [x] update rgb-hex package (to 2.1.0)
• [x] remove camel case filenames by hyphenating all filenames
• [x] add some simple unit tests
• [x] add CI
• [x] add a precommit lint & test hook