Chore: Extract out code and use denim.

[ryan-roemer]

• Abstract out all lib / test files and use denim. Extract abstract template engine out. #37
• Leave builder-init
• Update docs and deps.

/cc @kenwheeler @exogen

[coveralls]

Coverage decreased (-5.9%) to 87.179% when pulling 1460323 on chore-denim into f906b7d on master.

[ryan-roemer]

Released in builder-init@0.4.0