Don't show h1s in module page table of contents (#949)

Closes #932.

We decided:

1. We are going to keep showing h1s for class and function pages. It's
useful because they have non-trivial code at the top level, like their
docstring and constructor. It's nice to have the quick way to access the
value.
2. For now at least, we won't show h4s in the module pages. There are 8
module pages in the current API docs that use h4s. I think showing h4s
improved ~3 of them, and made ~5 worse. So, for now, let's not include
them. This can be revisited, especially after
#942.

This regens all APIs but reverts dev docs, which have unrelated changes
and will be regenerated in a dedicated PR.

Author: Eric-Arellano