Changes "use base" to "use parent" everywhere.
Parses HTML with the ignore_unknown flag set to 0, so that HTML5
elements can be recognized.
Adds "parent" field and related methods to Node class.
Adds missing Scalar::Util import.
Adds match_creator method; refactors it with preexisting match_* methods.
Updates default rendering logic to call parent node's render method.
Code cleanup.