Serializer simplifications after IMPLEMENT_SERIALIZE overhaul
Rename IMPLEMENT_SERIALIZE to ADD_SERIALIZE_METHODS
Use OR of respective block flags for masks
Remove DNS Seeds run by entities which were never well-established.
Merge pull request #4671

550d4fa Remove DNS Seeds run by entities which were never well-established. (Matt Corallo)
Merge pull request #4820

910526d Use OR of respective block flags for masks (Pieter Wuille)
Merge pull request #4808

3f6540a Rename IMPLEMENT_SERIALIZE to ADD_SERIALIZE_METHODS (Pieter Wuille)
47eb765 Serializer simplifications after IMPLEMENT_SERIALIZE overhaul (Pieter Wuille)
Create build-aux/m4 dir. Move m4 scripts for out-of-src builds.
Remove pkg.m4. Update .gitignore.