Cleaning up directory manager interface.

MODEL: there is such a thing as the 'directory manager interface'. It currently
looks like this:

    add_assets_to_repository()
    commit_assets_to_repository()
    copy()
    display_present_working_directory()
    display_repository_status()
    doctest()
    list()
    list_long()
    pytest()
    remove()
    rename()
    update_from_repository()

It will soon look like this:

    add()
    commit()
    copy()
    doctest()
    list()
    list_long()
    pwd()
    pytest()
    remove()
    rename()
    status()
    update()