Fix #286 PHP namespaced params are missing the `\` namespace characters 

Fix https://github.com/spadgos/sublime-jsdocs/issues/286

I'm not sure if there was a reason the `\` character was skipped when parsing arguments. PHP namespace character is `\`.

I was [unable to run the tests](https://github.com/spadgos/sublime-jsdocs/issues/307), but have added a test based on the existing ones. It should pass.