Adds support for connecting to both 1.12.2 and 1.11.2 (protocols 340 and 316) servers
https://github.com/iceiix/steven/issues/18 Enhance protocol support
Closes https://github.com/iceiix/steven/pull/48 1.11.2 protocol support (316)
* Restore create_ids!() macro in packet identifiers
* Add translate_packet_id() function to map external 1.12.2 packet ids to internal sequential ids
* Implement translate_internal_packet_id() from a new protocol_packet_ids! macro
* Move packet IDs to separate file, v1_12_2.rs
* Change supported protocols constant to an array
* Add v1_11_2 protocol packet IDs (from https://github.com/iceiix/steven/pull/48)
* Add keep alive packet variants: _i64 (>=1.12.2) and _VarInt (<=1.11.2)
* Abstract protocol versions, can now connect to both 1.12.2 and 1.11.2
* Send protocol version in handshake packet
* Restore 1.11 (315) protocol support as in original (https://github.com/thinkofname/steven) Steven