Update credit parsers to use Wordpress's HTTP API

Hello,

I've just had a go at updating this plugin to use the official WP HTTP API ( http://codex.wordpress.org/HTTP_API ) rather than it's existing curl mechanism. 

We needed this on our end in order to make use of WP's centrally configured proxy settings (everything outbound needs to be proxied in our current setup), and the existing curl set up didn't appear to facilitate this.

Does this sound like something you'd be interested in pulling centrally? (as i suspect this may potentially be of use to others with similar setups to our own also).

Thanks,
Carl

P.S. I also fixed a minor css bug & an undefined index we sometimes saw when trying to pull in none existing credit date.