Changes:

* Updated to minecraft 1.15.2.
* Added NetIdBase.withTinySize, withNormalSize, withLargeSize, withoutBuffering
    * These are equivalent to setTinySize (etc) but return the NetIdBase object itself.
* Implemented NetIdBase.notBuffered() - now it actually does something!
    * Also allowed the buffering flag to be changed at any time - as it doesn't need to
      be stable over time.
* Added NetIdBase.toClientOnly, toServerOnly, and toEitherSide:
    * These check to see if they are being sent from the correct side when sending them
      and check when they are received.
