Expose the Sphinx logs to maintainers

[stof]

There are 2 different levels where it needs to be exposed:

• Sphinx errors, which are making a build fail (to explain why it failed). The domain currently has this info in the message of the BuildFailedException, but we might want to refactor this to get it in a better way
• Sphinx warnings, which don't make the build fail but maintainers might still want to fix them to avoid quirks in their documentation. There is no way to access them in the current domain.

[everzet]

Cool idea. But lets discuss it further after initial release.

[stof]

This is my plan. This is why I haven't set the milestone on it

[everzet]

got it :)