Prevent creation of PR Card if related Issue Card exists in Project #4
Description
This feature might go best as an optional argument to command new_pullrequest where if the argument exists, it checks to see if there is an issue mentioned in the body of the PR (e.g. Fixes #[issue_number], other wording variations recognized by GitHub that have GitHub auto close the issue if the PR is merged) and if an issue is mentioned, it skips the creation of the PR project card.