There are a few major modes which are not based on prog-mode, that I
want to behave like prog-mode. Previously each did nearly all the same
setup that's done via the prog-mode hooks. Now instead let's actually
run runs the hooks for prog-mode.
- Switch from highlight-indentation package to highlight-indent-guides.
- Activate visual indentation in a prog-mode hook, rather than doing
within each individual major mode. It was already done within all
major modes based on prog-mode anyway.
- Add new siren-display-indetation module and function as a central way
to enable visual indetation guides. This makes switching the
underlying package at some point in the future much easier.
