Places div.speaker-notes in default kbd Tab order, and when focused,
prevent slide navigation with up/down arrows, allowing up/down arrow
keys to scroll div.speaker-notes.

Simplify full setup

`./*.md` didn't work `*.md` does work

Fixes #1549, now UA match is limiting out MS Edge and Chrome detection is improved. Also improved UserAgent access by storing it in to a local variable, it was accessed so many times in different places.

readme tweaks

Table of contents added in README.md

Make PDF export section less OS X specific.

Closes #1073.

Fix query parameter issue in notes plugin.

Remove unused dependencies.