Add precommit hook for checking for merge conflicts
Add dev dep for blacken-docs
Add dev dep for pre-commit-hooks
Update all precommit hooks to use system language
Update toxfile to use new dev deps
Fix tox vs. precommit conflicts with reorder-python-imports
Poetry 1.1 is due any day and when it does much of the functionality this
module uses will be moved to poetry-core. Until this module is updated
to use poetry-core 1.1 will be a breaking change