Added conditional compilation so it works for Lua 5.1, 5.2, 5.3

Makefile

@@ -1,7 +1,7 @@
 # makefile for immutable table library for Lua
 
 # change these to reflect your Lua installation
-LUA= /users/Bruce/Sandbox/Lua/lua-5.1.5
+LUA= /users/Bruce/Sandbox/Lua/lua-5.3.4
 LUAINC= $(LUA)/src
 LUALIB= $(LUA)/src
 LUABIN= $(LUA)/src

limmutable.c

@@ -13,6 +13,14 @@
 #define MYNAME "immutable"
 #define MYTYPE MYNAME
 
+// API changes from 5.1 to 5.3
+#if LUA_VERSION_NUM >= 502
+#define lua_objlen(L, i) lua_rawlen(L, i)
+#define lua_equal(L, i, j) lua_compare(L, i, j, LUA_OPEQ)
+#define luaH_getnum(t, k) luaH_getint(t, k)
+#define luaL_register(L, _, R) luaL_setfuncs(L, R, 0)
+#endif
+
 // Class:new(...)
 static int Lcreate_instance(lua_State *L)
 {