Add plugin loading/processing module
Allow event hooks to be passed in to load_plugins
Created main() function in clidriver

This gives room for the plugins to be loaded, rather than
have CLIDriver know anything about the plugin loading process.

As a result, I've updated aws and aws.cmd to use clidriver.main()
instead of creating the CLIDriver instance themselves.
Bug fix, add emitter to main()

Not loading any plugins currently.