Preliminary definition of Translator behaviour

Modules implementing the Alembic.Translator callbacks will be
responsible for reading packets from, and writing packets to,
individual clients. Each client will be associated with a single
such module; that module will implement the details of a
particular networking protocol, keeping these details isolated
from the rest of the Alembic codebase.
Minor cleanup: use pipe operator for concision
Add preliminary typespecs to Translator module

At some point in the future, a separate module will probably be
created to wrap more explicit specifications of the 'request'
and 'event' types in particular. These types will likely end up
being defined in terms of their subtypes, i.e. the exact sorts
of requests and events that make it into the standard API.
Minecraft.Protocol module implements Translator callbacks

As the test case for the client-agnostic approach I've been
taking to Alembic development, the Minecraft.Protocol module will
also be the reference implementation for the Translator behaviour.