[editorial] markdownlint in less then 1.5 sec

[chalin]

• Adds a Gulp task named lint-md to run markdownlint
  • The task runs in less than 1.5 seconds over the same files as the markdownlint make target, which takes much longer, when run from the command line
• Fixes the errors reported by markdownlint Gulp task. I'm unsure why, with the same config, the CLI misses those errors
• Replaces the call to the markdownlint CLI with the Gulp task in the markdownlint job

[chalin]

As you can see from the GH actions above, the new Gulp task takes 17s to do markdownlint checks (that includes running npm install).

[joaopgrassi]

I don't have experience in gulp but I'm all in for making the check faster, that's great! Just one thing, could we also make it use the same in the make task markdown-link-check?

[chalin]

... also make it use the same in the make task markdown-link-check?

@joaopgrassi - done

[jsuereth]

Thanks for this! Markdownlint's time was pretty insane before.