Merge Ishowu plugins

[joseph]

The Ishowuhd plugin is almost identical to the original ishowu plugin. However, it seems to have some useful updates.

I'd like to see the improvements in the new plugin merged into the original where applicable, and then some way of indicating to the plugin whether you want to use IShowU or IShowU HD. This is probably just a method call: use_ishowu_hd or something.