use prefix arguments to scroll by individual lines
When narrowed to a subtree `epresent-run' will restrict the presentation to the current subtree.
Thanks to Geert Kloosterman for this patch.
note that latex image preview may require some additional Org-mode configuration, and the presence of specific commands (e.g. dvipng) on your system
to use call `epresent-run' from inside of an Org-mode buffer