Separate Travis Builds

Travis supports running a matrix of separate builds. This (a) paralellizes the build process and (b) makes it easier to see when the specs are failing on one particular environment (set of dependencies).

This commit

 1. introduces a new "test" task that runs `script/run` against the current environment (with no prerequisites) and uses that in Travis
 2. eliminates Travis builds on Node 0.11. That build was mostly redundant since this project isn't terribly sensitive to changes in Node.js.
 3. moves all dependency installation on Travis into its install step
 4. adds a long series of test configurations to the `travis.yml` `env` matrix

References:

 * http://docs.travis-ci.com/user/build-configuration/
 * http://docs.travis-ci.com/user/caching/
 * http://docs.travis-ci.com/user/languages/javascript-with-nodejs/

cc @chrmod @rwjblue