Switch test setup to Karma

A variety of changes that result in a new and improved (IMO) test setup:

* Switch to using the [Karma](http://karma-runner.github.io) test runner. It wires up the test specs, library code, and test framework. All you need are a couple of config files. Also means we are actually testing against the client-side libraries Bower is installing, rather than duplicates in the test directory.

    Testing that Flight works with jQuery 1.9.x or 2.0.x should now involve just this:

    ```
    bower install --save jquery#1.9.x
    make test
    ````

   The reason you'll see 74 tests in the CLI output instead of the 70 currently being run is because Karma automatically picked up the `fn_spec` test that appears to have accidentally been missed out in the current setup.

* Configure Travis CI to install Bower and Bower packages before running tests. Also get it to run tests in Node.js 0.10 as well as 0.8.

* Add development notes to the CONTRIBUTING.md so others can get the test environment setup.

* Some small, related cleanup tasks in the docs, `package.json`, and `.gitignore`.

You still run the standalone build and tests with `make test`, it just passes through Karma instead. To be able to run the CI tests on our Twitter laptops, Karma needs to know where to find PhantomJS (since we use a custom install location for Homebrew). Add this to your `.bash_profile` or your local bash settings file:

`export PHANTOMJS_BIN="$(brew --prefix)/bin/phantomjs"`

As an added bonus, during development, you can just run `karma start` (if you also install Karma globally: `npm install -g karma`) and it will watch the Flight lib and test files, re-running them automatically in both Firefox and Chrome.

Let me know if I've missed anything.