Add tests for Series

Adds some basic tests for the series, including extracting data,
filtering and ordering.

Some of these fail, because we don't have a default keyFunction or
valueFunction, so they don't handle lists of numbers very well.
Add Travis for CI

Adds the basic travis configuration, to specify that we are a node_js
project.
Merge pull request #46 from tpkelly/master

Add tests and CI