Consolidate the code in our custom markdown processor
    
    With this commit we are consolidating all the pieces of code needing to
    extract the namespace, project name and user name corresponding to the
    page displayed in a single place simplifying the maintenance of said
    piece of code and avoiding to fix bugs in multiple places.
    
    This simple consolidate fixes automatically linking to a commit by
    providing its hash in markdown.
    
    Fixes https://pagure.io/pagure/issue/2612
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>