repoman/main.py: Create errors.py

Move warn() and err() into errors.
repoman/main.py: Create modules/commit/repochecks.py

Move some code that checked for being in a commit-able repo.
repoman/main.py: Move caterror to repoman/errors.py
repoman/main.py: Move another commit check to modules/commit/repochecks.py
repoman/main.py: Create repos.repo_metadata()

Move code to a new function in repos.py.
repoman/main.py: Remove uneeded textwrap import