New feature: make floating TOC, also add options

[aloneguid]

In addition to my previous comment #2 I have done it for myself and sharing if you want to merge.

I've added options to the browser button to turn on and off sidebar and TOC:

TOC is moved out of page top and becomes a floating overlay on top-right:

I had to change your css because it's now enabled partially based on options selectors.

The manifest has two additional permissions:

• "storage" - to persist user options.
• "tabs" - to reload current tab from the options dialog.

I've been using this for a day or so now, seems to be fine.

[merill]

This is awesome! Thanks for the PR @aloneguid