feat(packets): pass nullable to packet serializers

Merge pull request #45 from Rutherther/feat/mates

Add support for mates

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

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

fix(packets): syntax error in generator

fix(packets): deserialize strings starting with "-" correctly

feat(serializer): fix null representation as stated in #18

feat: split packets definitions into separate assembly