Merge pull request #47 from Rutherther/feat/pass-nullable

Pass CanBeNull to string serializer and converter

fix(packets): correctly handle nullables in NullableStringConverter

feat(packets): pass nullable to packet serializers

fix(packets): add missing usings

chore: move PacketSerializer types to correct namespace

fix(packets): seek when nullable converter finds null.

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

feat: split packets definitions into separate assembly