Amend PHP completions to match draft PSR-5

The [(currently draft) PSR-5](https://github.com/phpDocumentor/fig-standards/blob/master/proposed/phpdoc.md) document aims to standardise the tags available in phpDoc. DocBlockr should only support those tags. If any developer really wants to use other tags, then they can create their own local auto-completion extension.

This PR might be better waiting until the PSR is finalised, but this at least puts it on the radar and allows time for any discussion.