Add Travis CI support

Tests most aspects of the library at every commit and pull request.

After merge requires activation [here](https://travis-ci.org/profile/ShareKit).

Sample output for this pull request [here](https://travis-ci.org/rivera-ernesto/ShareKit). Fails because of pending pull requests and failing unit tests.

Supersedes #912.
`pod lib lint` on the other hand exercises the current code.