[REQ] Provide map CRC through A2S queries

[MegaBrutal]

It would be great to be able to query the CRC of the currently running map from servers through the A2S protocol (preferably not breaking existing queries and responses). The reason for this is that map names are not enough to identify maps; there might be different versions of the map, or it's even possible that different map authors accidentally came up with the same map name.