cautodoc_transformations does not "pickle" nicely

[jnikula]

Sphinx automatically pickles and caches the configuration, speeding up processing if there are no changes. Unfortunately, pickled function references in cautodoc_transformations are bound to change. This leads to re-reading of the source documents:

updating environment: [config changed ('cautodoc_transformations')] 5 added, 0 changed, 0 removed
reading sources... [100%] syntax

This is quite an unfortunate unintentional consequence of the transformation mechanism.

[jnikula]

One idea is to use Sphinx events for the transformations, so that you could actually write independent Sphinx extensions for the transformations. app.add_event('cautodoc-transform') and app.emit_firstresult('cautodoc-transform', comment, transform) in Hawkmoth side, and app.connect('cautodoc-transform', transformation_function) in the extension implementing the transformation.

It's a bit sad I didn't think of this before implementing the current transformations, leading to another round of deprecations and changes.