add documentation of threaded to client docs

This is based on the documentation added to the 2.4.0 release notes.
Add publish_timeout to client docs

This is based on the documentation added to the 2.4.0 release notes.
Add soft_shutdown to server docs

This is based on the documentation added to the 2.5.0 release notes
Merge pull request #228 from richardc/release_notes_into_docs

Convert release notes examples into docs