Add server.on as a shortcut for hooks.add

[dblock]

Add server.on, eg.

server.hooks.add(:hello, MyBot::Hooks::UserChange.new)

could become

server.on :hello do
  # implementation
end

cc: @dramalho, thoughts?

[laertispappas]

I think that hooks method and the Set implementation should be deprecated as well since they are implementation details and should not be part of the public API.

I would like to prepare a PR and add the on shorthand that you proposed. What do you think about the deprecation that I mentioned above?

Best
LP

[dblock]

I'd like to see that code.

[dblock]

Resolved via #147