Merge pull request #4737
31e9a83 Use CSizeComputer to avoid counting sizes in SerializationOp (Pieter Wuille)
84881f8 rework overhauled serialization methods to non-static (Kamil Domanski)
5d96b4a remove fields of ser_streamplaceholder (Kamil Domanski)
3d796f8 overhaul serialization code (Kamil Domanski)