added disconnect reason

[1zun4]

Hello there,

with this PR I have added the possibility to catch disconnect events and their reason easily.

But here is an issue that I am facing and cannot figure out how to fix:
When the server disconnects us from the game, we normally get ClientboundGamePacket::Disconnect but the connection is closed before we can read the packet and fire the event with an reason. This causes us to not get the actual disconnect message and I really need HELP with this issue.

[1zun4]

How it should look like (disconnect by Velocity).

How it fails (disconnect by plugin):

Seems Velocity, when disconnected by plugin, sends it as ClientboundCustomPayloadPacket, that explains why I could not capture it as ClientboundGamePacket::Disconnect.

Edit: Might handle custom payloads (as disconnect), for my use-case this CCBlueX@86db681 is enough. Also might not parse it already, as it does not always use the standarised ResourceLocation format.

[mat-1]

Thanks! I'm changing the reason to an Option<FormattedText> after merging this though since there's some cases where the user will want to format the text another way. Also I noticed a couple bugs with disconnecting while testing this but those are totally my fault.