Refactor Client module for generality

We're finally able to remove all specific references to the
Minecraft protocol translator module from the generic Client
module; the Client module, like many of the other modules we've
recently refactored, is now protocol-agnostic.

I've also taken this opportunity to clean up some of the ExActor
code in the Client module, increasing the readability of said
code by a good amount.
Cleanup: remove unneeded aliases

Referring to functions defined by a module within that same
module obviously doesn't require an alias (I don't know what
I was thinking). We also don't need to include an alias for
a module that only gets referenced once.
Improve readability of PluginLoader module

The PluginLoader module now contains additional documentation and
cleaner, more idiomatic code.