fix(packets): correctly use cast id instead of vnum in UseSkill packet

Merge pull request #8 from Rutherther/game-objects

Game objects

fix: implement IPacket in use skill packets

feat: split packets definitions into separate assembly

Merge pull request #12 from Rutherther/packets

Implement custom packet serializer

feat: enable inline converters in all packets

feat: add packets (ncif, u_as, pusle, msg, say, st, stat, c_mode, lev, ski, sr)