Properly export all lua-facing functions and use those for initialization (love.cpp no longer explicitly mentions implementations)

src/modules/physics/box2d/wrap_PulleyJoint.h

@@ -37,7 +37,7 @@ namespace box2d
 	int w_PulleyJoint_getLengthA(lua_State * L);
 	int w_PulleyJoint_getLengthB(lua_State * L);
 	int w_PulleyJoint_getRatio(lua_State * L);
-	int luaopen_pulleyjoint(lua_State * L);
+	extern "C" int luaopen_pulleyjoint(lua_State * L);
 
 } // box2d
 } // physics