Added plugin to support megacrypter.com

Implemented as hoster instead of crypter because I couldn't find an easy way to hand the file decryption key and the download URL to the MegaNz plugin. (Real MegaNz URL is never known).

Right now it doesn't support password protected megacrypter URLs.

Tested with some files. Works well thus far.

Feedback welcome.
Merge pull request #153 from gonzalosr/patch-1

Added plugin to support megacrypter.com