Redis Functions - Added redis function unit and Lua engine

Redis function unit is located inside functions.c
and contains Redis Function implementation:
1. FUNCTION commands:
  * FUNCTION CREATE
  * FCALL
  * FCALL_RO
  * FUNCTION DELETE
  * FUNCTION KILL
  * FUNCTION INFO
2. Register engine

In addition, this commit introduce the first engine
that uses the Redis Function capabilities, the
Lua engine.

src/script_lua.h

@@ -57,10 +57,11 @@
 #define REGISTRY_RUN_CTX_NAME "__RUN_CTX__"
 
 void luaRegisterRedisAPI(lua_State* lua);
-void luaEnableGlobalsProtection(lua_State *lua);
+void luaEnableGlobalsProtection(lua_State *lua, int is_eval);
 void luaSaveOnRegistry(lua_State* lua, const char* name, void* ptr);
 void* luaGetFromRegistry(lua_State* lua, const char* name);
 void luaCallFunction(scriptRunCtx* r_ctx, lua_State *lua, robj** keys, size_t nkeys, robj** args, size_t nargs, int debug_enabled);
+unsigned long luaMemory(lua_State *lua);
 
 
 #endif /* __SCRIPT_LUA_H_ */