util -> util/must: Refactoring.

- Methods got renamed:
* MustRead* -> Read*.
* MustWrite* -> Write*.
types/minecraft: Fix refactored import paths.

- util.RWErrorHandler -> must.ReadWriter.
proto/packet: Refactoring.

- Methods got renamed:
* MustRead* -> Read*.
* MustWrite* -> Write*.
proto/packet: Fix refactored import paths and methods.

- PacketErrorHandler -> MustReadWriter.
- Use new method names:
* MustRead* -> Read*.
* MustWrite* -> Write*.
Add pkg: minero. Root package.
Move latest MC Protocol supported to root pkg.