Implement server side disconnect packet

[PabloMK7]

Implements the method Disconnect in PRUDPEndPoint, which allows disconnecting a PRUDPConnection by sending it a DISCONNECT packet. The connection will be cleaned up after it times out or a disconnect acknowledgement packet is recieved back.

[DaniElectra]

I don't think we need this? We already have the "connection ended" event anyway

[PabloMK7]

The emit? What's it's purpose anyways?

[jonbarrow]

The purpose of emit is to send event signals to listeners. We don't personally make use of all of them, but another developer may find them useful in their own servers (such as more detailed logging at the packet level). The syn, connect, disconnect and data events are emitted when packets of those types are received. Though looking at the code again, we only expose the disconnect and data packet events (in previous versions of the library the On method was exported and could be used to listen for any packet type, but this was removed in favor of specific OnData and OnDisconnect methods)

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