Coroutine support for Mudlet's C API functions

It is currently impossible to call Mudlet's C api functions from coroutines, because they all follow this design pattern:

Host * pHost = TLuaInterpreter::luaInterpreterMap[L];

Where the associated host is retrieved from a map of Lua states. coroutines have their own Lua state, and thus the proper host is not locatable from a coroutine calling a Mudlet function.

A fix for this would be to convert all functions to instead store and retrieve the host from the VMs registry, because coroutines share it.

http://www.lua.org/pil/27.3.1.html