feat(packets): pass nullable to packet serializers

Merge pull request #46 from Rutherther/feat/act4

Add Act4 status processing

feat(game): emit Act4StatusReceived event upon receiving act4 info

Resolves #43

feat(packets): add use partner skill packet

Merge pull request #45 from Rutherther/feat/mates

Add support for mates

fix(packets): correctly represent finfo

fix(packets): make nullable wrapper a class

feat(packets): add nullable wrapper to represent a compoud type that may be null as a whole

fix(packets): correctly deserialize list with generic elements inline

chore(game): add missing documentation

fix(packets): correctly deserialize list with nullable elements inline

feat(game): add mates processing

feat(game): add revive handling

feat(game): add friends processing

feat(game): add group processing

fix(packets): finfo contains just one update

feat(packets): add party stat packet

feat(packets): add pet and partner skill packets

feat(packets): add pclear packet

feat(packets): fix pinit packet for various entity types