(PDB-871) Prepare for 4.0.0 release

Bumped versions of dependencies, removed support for older
version (since this is a major release boundry)
(PDB-871) Typo in README.md

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #142 from kbarber/ticket/master/pdb-871-4-0-0-release

Ticket/master/pdb 871 4 0 0 release