Minor API, Documentation, and Testing Environment Improvements

Hi, @jmhodges!  I've used Levigo quite a bit, and I want to volunteer a couple of cleanups to improve user experience.  I've kept each change atomic as a separate self-standing commit; but if you want, I can squash them together into one.  For ease and speed of review, I have included the rationales in each commit log message.

A major improvement is the inclusion of automated testing with Travis, which works: [![Build Status](https://travis-ci.org/matttproud/levigo.svg?branch=refactor%2Fminor-polish)](https://travis-ci.org/matttproud/levigo).

The only thing you would need to do, should you accept this pull request, is to manually enable Travis CI for jmhodges/levigo in your project setup.  Nothing in this pull request relies on my configuration, except for this pull request description.  :-)