Update README.md

Link to Matthijs' postgresql connector and minor updates in the examples
Adjusted api to recent changes.
Merge branch 'master' of https://github.com/rbock/sqlpp11
Merge branch 'release/0.17'

Conflicts:
	README.md
Merge tag '0.17' into develop

Lower threshold for experiments by removing generation of Sample.h from CMakeLists
Added link to wiki
Added link to container backend