Feature Request: Table of Contents

[anonimitoraf]

Hi!

First of all, thank you for all your work on this. It's so damn cool.

Secondly, would it be hard to support a "Table of Contents" like so:

?

I don't mind implementing it but since I've not used Hugo before, I don't know whether this is even possible to do(?)

[anonimitoraf]

Actually, I've started work on this

I'll make a PR when I finish :)

[anonimitoraf]

Update:

I think the last thing I need to do is to make the header sticky