feat(packets): add entities and maps packets

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

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)