Add more issue closing patterns

Following https://docs.gitlab.com/ee/user/project/issues/managing_issues.html#default-closing-pattern. This doesn’t implement everything that GitLab does, because I only have a minute and don’t want to rework and test the regex right now.

However, this does add support for the more-commonly used ‘Resolves’ and (to a lesser extent) ‘Implements’, so it is a slight improvement.

Signed-off-by: Philip Withnall pwithnall@endlessos.org