Add unit tests, and continuous integration

[tjbenton]

Since this library has grown to accommodate several different functionalities there needs to be unit tests as well as comparison tests. Comparison tests are to ensure that things are outputting correctly but this will be a little tricky since we're dealing with random data so some sort of testing helper will need to be created for these.

This will be done using ava, and ava-spec. The continuous integration will be done with travis ci.

• [x] cli.js
• [x] documents.js
• [x] index.js
• [x] input.js
• [x] models.js
• [x] output.js
• [x] output/
  • [x] console.js
  • [x] couchbase.js
  • [x] default-options.js
  • [x] folder.js
  • [x] index.js
  • [x] sync-gateway.js
  • [x] zip.js
• [x] utils.js