Enforce style of commit messages

[Robbert]

• End with punctuation, rather [.…] than [?!].
• Include reference to bug tracker issue.
• Limit first line of the message to the GitHub cutoff of 70 characters.
• Warn to move files in separate "chore" commits.
• Require newline between first line and other content.

Ideally the commit message equals the issue subject.

Later on:

• Spell checking (depends on Use a spelling checker with a custom technical dictionary #53)
• Validate MarkDown

[Robbert]

Incomplete list of verbs a commit message (a task description) may start with...

Bug fix:

• Fix

Feature:

• Test
• Verify
• Add

Refactorings:

• Refactor
• Rename
• Move
• Remove

Configuration changes:

• Ignore
• Allow
• Disallow
• Enable
• Disable
• Configure