PHPdoc and php codesniffer corrections

When using htmlpurifier in my IDE, it flags lots of errors that are just phpdoc errors or omissions. For example it's really common for `@param` values to be missing a type, and it's picking up the first word of the comment as the type, which is nearly always wrong. There are lots of missing `@var` and `@return` properties, which leads to poor static analysis.

I also fixed some php code sniffer problems that were flagged, generally towards PSR-2 coding standards. There are no functional changes at all, just code layout and adding {} wrappers in some places.

So far I've only really touched the root and config classes since they are the ones most commonly dealt with.

Do you intend to push HTMLPurifier towards any particular coding standard? Are you happy to accept these kind of changes? If so, I'll do more.