feat(packets): add pet and partner skill packets

chore(packets): add documentation for ski packet

Merge pull request #32 from Rutherther/combat

Add combat extension

fix(packets): Add new unknown field to ski packet, make rank of SkiSubPacket optional

fix(packets): make cancel unknown nullable

feat(packets): add cancel packet

feat(packets): add entities and maps packets

docs: add documentation for missing fields

fix(packets): use skill vnum instead of id to avoid confustion between cast id and skill vnum

feat: split packets definitions into separate assembly