Move Pod::Html::_unixify to Pod::Html::Auxiliary::unixify.
Add file to test unixify().
Move relativize_url() to Pod::Html::Auxiliary.

Add a test file -- currently just a placeholder -- for relativize_url().
Start to encapsulate package-scoped variables.

Create a $self (hashref) and stuff 18 package-scoped 'my' variables into it.
$self will eventually become an object.
Move @Podpath into $self.