Add circleci integration

[viclim]

Fix #19

Not using workflow as there's no real advantage of using it here.

Build will now fail if code coverage is less than 100%.

[coveralls]

Coverage remained the same at 100.0% when pulling 37900e3 on RapidRiverSoftware:issue-19-add_circleci into 842ad36 on GSA:master.

[viclim]

Removing .travis.yml doesn't seems to stop travis from building this. Probably related to this https://blog.travis-ci.com/2014-03-05-repository-settings

[viclim]

coveralls is generating the error below in CircleCI

...
[Coveralls] Submitting to https://coveralls.io/api/v1
Coveralls encountered an exception:
RestClient::UnprocessableEntity
422 Unprocessable Entity
...
{"message":"Couldn't find a repository matching this job.","error":true}

It might be the switch from Travis CI to CircleCI that trip coveralls up.

[viclim]

The circleci badge is showing failing in https://github.com/RapidRiverSoftware/jobs_api/tree/issue-19-add_circleci. That's because the badge is showing the build status for master branch, and there's no build in circleci for the master branch.

[nickmarden]

Repush please @viclim? I've disabled Travis CI.