Keeps disabled buttons out of kbd tab order and indicates to assistive
tech like screen readers that button is disabled. Otherwise buttons
that aren’t enabled remain in kbd Tab order and screen readers announce
them as buttons, but they don’t work.

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.