[WIP] #40: Documentation Standards

I have created a baseline of handling Documentation Standards. phpDocumentor now supports rulesets in the same way as PHP_CodeSniffer and as such allows the custom creation of standards.

With this feature it will be possible to finetune and tweak how your documentation is validated.

This PR is still a work in progress as several features have not been added yet:

- [ ]: Setting a Standard from the command line by name
- [ ]: Setting a Standard from the command line by file name (separate ruleset.xml)
- [ ]: Read a Standard from the phpdoc.xml
- [ ]: User documentation
- [ ]: Fully covered by unit tests
- [ ]: Move basic standards package to a Components folder instead of Plugins