YAML configuration

Allows for (optional) `protractor.yml` file to be placed in config folder of a Rails project.

Configurable options:
* `port` (defaults to **4000**)
* `config_path` (defaults to `spec/javascripts/protractor.conf.js`)
* `startup_timeout` (defaults to **6**) -- this is the time in seconds that protractor-rails will wait for your rails server to start up

`protractor.yml` is parsed as ERB and as such may include embedded ruby code.