Add model summaries to documentation

[leonoverweel]

Feature motivation

Oftentimes when I want to find something like a standard model's layer name or its shape, I've had to build the model, wait for it to show up in my terminal, and then ^C out to stop it from training. It'd be much more convenient if these were saved somewhere for our standard models.

Feature description

A folder of .txt files with the output of that model's larq model summary, with links to those files on relevant docs pages.

Feature implementation

This could be implemented similar to the activation plotting we currently already have in the docs.

[AdamHillier]

This is actually not a bad way of testing that we haven't broken the models as well. Can do snapshot tests where we print the summary.

[leonoverweel]

Closed by #151.