Added int64 support to the script engine (#4522)

Added support for signed 64 bit integer value computation into the script engine.
This is required because newer official features require support for bigger numbers inside the scripts.

This also cleans up a lot of messy code and fixes a few issues like script stack corruptions.

Thanks to @aleos89 and everyone who supported me with this.

src/map/map.cpp

@@ -4517,7 +4517,7 @@ static int map_mapflag_pvp_stop_sub(struct block_list *bl, va_list ap)
 enum e_mapflag map_getmapflag_by_name(char* name)
 {
 	char flag_constant[255];
-	int mapflag;
+	int64 mapflag;
 
 	safesnprintf(flag_constant, sizeof(flag_constant), "mf_%s", name);