feat(markdown-renderer): option to normalize spacing after the list marker

[pbodnar]

This follows #197 and adds the possibility to switch ON the original renderer behavior when the space after list marker (called leader in mistletoe) collapsed just to 1 space.

[coveralls]

coverage: 94.153% (+0.003%) from 94.15%
when pulling b518edf on feature/option-to-normalize-space-after-list-leader
into 13d1c11 on master.

[pbodnar]

@allets, @anderskaplan, this PR follows the discussions from #197, provided you would like to give feedback. If no one protests in a few days, I would merge this to the master. :)

[anderskaplan]

lgtm!
just one thought about the naming of the flag, which is now very specfic. I believe that there are basically two modes you might want to run the Markdown renderer in: either you want it to stay as faithful to the original as possible, or you want the generated Markdown to be as regular (normalized) as possible. I can imagine that other options like this one will come, and maybe it's better to bundle them together with a single "normalize whitespace" option.

[pbodnar]

@anderskaplan, thanks for your feedback. So I would rename the flag to normalize_whitespace, with an outlook that we can gradually take this flag into account in more places of the renderer, right? I haven't studied the renderer thoroughly... :P

[anderskaplan]

@anderskaplan, thanks for your feedback. So I would rename the flag to normalize_whitespace, with an outlook that we can gradually take this flag into account in more places of the renderer, right? I haven't studied the renderer thoroughly... :P

yes exactly!

[pbodnar]

yes exactly!

OK, so I've generalized the newly introduced option. Hopefully fine now? :)

[allets]

@pbodnar, good!
Thanks for your commit that fixed my omission.
I like the idea of the generalization.
It works fine.