Proposal: Add support for decorator-based CommandModule command declaration

[richteer]

I see a lot of other python frameworks use decorators to define commands, routes, etc. I think it would be a good extension to include that in our framework as well, and may simplify some of the boilerplate for module developers.

Something like the following would be nice:

class TestModule(CommandModule):

    @command("test")
    def test_(self, msg=msg):
        self.reply(msg, body="Test!")

Here, the pair ("test", self.test_) would be automatically added to the module's self.commands dict, without needing to declare it in self.init() first.

Ideally, this should work with chaining other decorators, like hasPermission and AsArgs, as the command dec should not touch the parameters at all.

[richteer]

Note: this is tricky. Just attempted to implement this, and of course decorators are evaluated at "parse-time". We'd need to make sure these don't add themselves to a class-wide commands dict. Module instances should be able to have their own commands dict.