Make API docs more useful for basic users

[joewallwork]

One observation (that is not to be resolved here) is that our online API docs are no longer very useful for basic users and are instead geared at developers. In reality, all basic users want is the Interface docs, and the list they get above is somewhat daunting. There is an option to lost interfaces here but I don't feel it helps. I'm not sure if there is an easy solution to this and should perhaps create a new issue.

Originally posted by @jatkinson1000 in https://github.com/Cambridge-ICCS/FTorch/pull/225#pullrequestreview-2546456937