[lnet] Added luanet_pushlstring and luanet_pushstring to handle Unicode strings.
[lnet]Added  method get_main_state to get the LuaState from mainthread inside corountines.
[lnet] Fixed Debug Hook callback (usingn a cdecl) trampoline https://github.com/NLua/NLua/issues/56
[lnet] Fixed build https://travis-ci.org/NLua/lua/builds/28184500