jsonalchemy: memory engine search method addition

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
restful: `require_header` value checker addition

* Decorator accepts callable to test header value.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
access: jsonalchemy acl extension

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
documents: acl extension usage

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
documents: test coverage improvements

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>