Change commands from @gopher to !
There's now an interface for plugins, which simplifies handlmessage
quite a bit. Split all plugins into their own .go files. You still need
to manually register them in handleMessage.go
Adding !fortune command
Added an imgur plugin
Added help function to handleMessage
Added "Help()" to the Plugin interface.
Now all plugins implment a help function that returns usage and
handleMessage will return such usages if asked.
Added an initial, naive single config file.
It all gets loaded from gopher.cfg into the configMap global variable
that anything can access. Simple key=value file.