Fix podview, and a few cleanups to PodView and TextView

I've been looking closely at Prima::TextView for the last couple of weeks. I began working on revised documentation for Prima::TextView (not included in this patch) and in the process came across a handful of niggles and bugs. One bug is a series of warnings from PodView when and `=over` block is not followed by a distance, which I've silenced. The other is an issue with PodView's handling of `C<< $widget->method() >>` which ends up getting rendered as if I had said `C<< $widget-method()> >>`.

This pull request solves these two bugs, makes a few parts of TextView a little more legible by using named variables in place of `$_`, and adds a functioning Synopsis to TextView.