Class QtLuaEngine is a QObject subclass representing a Lua interpreter.
This object can be used to add a Lua interpreter to any Qt application
with capabilities comparable to those of the 
QtScript language
and additional support for multi-threaded execution.
Instances of this class can be in one of three state:
QtLuaEngine::Ready indicates that the interpreter
is ready to accept new Lua commands.
QtLuaEngine::Running indicates that the interpreter
is currently executing a Lua program.
QtLuaEngine::Paused indicates that the interpreter
was suspended while executing a Lua program. One can then
use the Lua debug library to investigage the Lua state.
Class QtLuaEngine provides member functions to 
submit Lua strings to the interpreter and to collect 
the evaluation results.  If these functions are invoked
from the thread owning the Lua engine object,
the Lua code is executed right away. 
Otherwise a thread hopping operation
ensures that the execution of a Lua program happens 
in the thread owning the Lua engine object. 
Class QtLuaLocker provides means
to directly access the Lua state 
lua_State* using 
the Lua API.