Convert http(s)-links to issue links
As seen in issue #1420 (closed) there are a lot of URLs listed such as
I expect such links to be converted to
MR !503 and
issue #1378 automatically if those URLs point to the same instance of GitLab as the short forms are better readable (beware, the link could also point to a specific comment). Same applies to links to commits (e.g. https://gitlab.com/gitlab-org/gitlab-ce/commit/a62dbd11cb14e6e96e89cc7e9f944072a0e9ed1a -> a62dbd11) and files (e.g. https://gitlab.com/gitlab-org/gitlab-ce/blob/6237cae1f16475d874ea761a62350344bdbff617/features/admin/deploy_keys.feature ->
/features/admin/deploy_keys.feature@6237cae1, here also
#L15 could be in the URL).