Functionality modification

Instead of having 3 identical caster pages with different shortcode att's
to display all, series, or type, I instead added the ability to pass
variables through the URL to $show, either "series" or "type". Now all of
the content can be on one page and the nav menu on the site simply links
to:

All Casters -> /casters/
Casters by Type -> /casters/?show=type
Casters by Series -> /casters/?show=series