Custom images support

[isukces]

First of all thank you for your plugin.
It would be great to have plugin with custom image handling. I think about following syntax
:http://server.com/image.jpg:
or with image size override
:640x480,http://server.com/image.jpg:

[jbevain]

It's a cool idea! I don't have time to work on this right now, but you're more than welcome to send a PR my way!