Documentation Failing to build on RTD

[bjlittle]

The documentation is failing to build, see here.

Previously, the documentation hasn't been built for over 20 months i.e., not since the 0.18.0 release.

😢

[tkknight]

This is disappointing, clearly this repo needs more ownership.

[tkknight]

PR to fix the docs build: #366

[pp-mo]

A fix for the problem has now appeared on main

But we still need work to create functioning v0.19 docs
That includes necessary manual changes to the docs themselves, like getting the main index page to say "v0.19" (!!!)

• which I guess will have to be released as 0.19.1

[pp-mo]

Fixed in ##370