bugfix: transaction rollback in SQLStore

Do not rely upon a contextmanager to implicitly rollback
transactions in response to failed queries. Handle explicitly with
try/except/else.
docs: fix alignment issue in README ToC
pep8 fixes for `corpus` sub-package
fix missing `CONFIG_NS` import in `corpus`
merge bug fixes from develop branch

Merge branch 'develop' into release/1.1.0