Fix formatting

[bbatsov]

This is a slightly meatier PR that:

• fixes all remaining files with Windows line-endings (there were just a handful of them)
• adds a default config for markdown-lint and CI job to run it automatically on files that were changed
• applies whatever formatting fixes could be made automatically

[bbatsov]

(note - the automatic check will fail for my PR, as we have a lot of files with long lines, but I think those should be addressed 1 by 1 down the road, instead of in bulk)