I slowly started to work on rstlint in its own tree because working in a single file felt inconfortable.

The more I advanced in this direction the more it made sense to me:

- I first added tests, I may have been able to do so in the cpython tree though.
- It would ease the publication of it to pypi.org so it can be used by other projects.
- It may ease contributions (some non-core-devs could be given rights to the repo, which make sense as it's not really Python related but more Sphinx related).

It currently looks like this: https://github.com/JulienPalard/sphinxlint but should obviously be moved to github.com/python/ if we adopt this direction.

So what do you think? (cc Georg as the main author of the script)

If so I'd also like to rename the thing, it's currently named `rstlint`, but it's more a `sphinxlint` as Sphinx has adds a lot to rst and existing rst linters does not handle Sphinx well.