Create script to generate various TOCs

[maneesha]

Right now, we have TOC-like content in several places:

• Part of index page
• Left sidebar
• Top dropdown menu

Currently these are all hard-coded, so when one changes we have to update all manually. This can be better managed by a function in conf.py that takes a list or dictionary of handbooks and returns html content for each of the elements listed above.

See example.

[maneesha]

Noting here that this can also be used to address #14

[maneesha]

Closing this because we don't actually have all those menus anymore.