BadExpectedAccess is not a LuaException #108
Description
The fact that BadExpectedAccess is not a LuaException is turning out to be a big issue for me. Errors inside callbacks are caught based on being LuaExceptions. That allows proper throws from C++ to Lua's C longjump and back to my code's C++ environment safely, unwinding all the way out without crashing.
This is also a breaking change. Runtime errors in LB2 generate LuaExceptions. LB3 throws BadExpectedAccess which is currently plain std::exception, though I have proposed it (in #104) as a std::runtime_error in order at least to get a message. But now I'm thinking it should be a LuaException. Or at least it should be transformed into a LuaException up the chain.