Workaround OS X quirk for shutil.rmtree

It doesn't like paths that end in "/."
autogen top-level index.html
trimming some fat
consistent formatting for offsite links in DL section
slightly better handling of embedded video elements

Get the YT params into the elements file.
missed a spot for YouTube ID substitution
fixes for full-size YouTube video embed

- Removed a couple of deprecated URL parameters.
- Don't need to reserve space for YT control bar these days.
add a mods section
wordfiddling
Move popups higher on the page