Add phpDocumentor configuration

This is the bare essentials for phpDocumentor.

Simply run `phpdoc` from the `/docs/` folder.

To customize, copy the `/docs/phpdoc.dist.xml` to `/docs/phpdoc.xml` and make your desired changes, then run `phpdoc` to regenerate. The `phpdoc.xml` file is your custom file and will be ignored by git.
Merge pull request #195 from drbyte/phpdocumentor

Add phpDocumentor configuration