Work in progress:

  - Move third-party libs from ./lib to ./vendor
  - Move braintree.js to ./src/braintree.js
  - package.json file for metadata and devDependencies.
  - Rakefile now parses package.json for version info.
  - braintree.js is now an AMD module which exports Braintree. It still uses
    window.Braintree namespace.
  - gulpfile
    - build vendor libs into UMD modules
  - update .gitignore to ignore node_modules, npm-debug.log
  - vendor libraries are now wrapped in UMD format.
  - vendor libraries are imported via AMD dependencies.
  - tests now load via AMD dependencies.
  - SpecRunner.html.erb template updated.
  - .jshintrc file.