Add initial Travis CI configuration file

The build is currently tested against Node versions 0.10 and 0.8, i.e.,
the two most recent stable versions.

Tests indicate that it fails when run against version 0.6, which is not
a concern at this time.

fix asylumfunk#45
Add build status image to README
Merge pull request #31 from asylumfunk/i/45

Add continuous integration build testing