allow for matching on any nickname mention

[crunchywelch]

sometimes we like to alert in channel with just the nick, without a proper @nickname mention, this allows for a broader match for any mention of the nick such as nickname: message this patch adds a broad_mention message event type which catches those instances

[anonrig]

Hey @crunchywelch

Thank you for your pull request. Honestly, it's really great the ability to send a broad_mention event upon a message that includes a username, but I am not really quite sure if this functionality should be added to the library itself or should be added to an example project itself.

What about we wait for other responses/thoughts in this manner? :)

[benbrown]

Let's use the version of this functionality in this PR:

#189