As part of #843 we're upgrading past Hugo v0.60 which introduced Goldman
as the Markdown handler, which has changed the way that the Table of
Contents is handled:

- we need to explicitly set the headings to include
- we want a `<ul>` not an `<ol>`
- we need to remove the manual `<a name>` as it's autogenerated now (and
  has been for some time)
- some `<a name>`s have been updated