Fix dhellmann's notes from April 18

removed the python 3 classifier. See note
https://github.com/malor/oslo.db/commit/e4cfa6d39d2aa53af64ab34de97183f98fbeb667#commitcomment-6058177

added W292 pep8 check. See note
https://github.com/malor/oslo.db/commit/276f7570d7af4a7a62d0e1ffb4edf904cfbf0600#commitcomment-6058296

added usage examples. See note
https://github.com/malor/oslo.db/commit/e4cfa6d39d2aa53af64ab34de97183f98fbeb667#commitcomment-6058130