Documentation improvements

The docs css needs to be improved to have consistent font sizes:

  1. the show_doc sig uses larger fonts than the rest of the html, so it’s a bit painful. I guess we need to tweak the .css to get to use similar fonts for mono and non-mono fonts.

  2. same for quoting - uses a much bigger font for blockquote, e.g. the top of fastai Abbreviation Guide – fastai