added dead-link checking

[maxwondercorn]

Resolves #77. Broken links can now be detected via npm run lint:links. This can be run manually as needed. It does not run in Travis-CI because it will always fail on http://localhost:4200. I will work on a PR for whitelisting in Remark - no timetable - and then can add the check to the other markdown linting.

npn run lint:md now has the --frail parameter and will fail in Travis-CI if spellchecking or other linting presets generate a warning.

Updated readme on markdown linting. We're probably 95% covered on spelling and I'm sure we will catch additional words with new pull requests.

If you like, I can do PRs on other guides to add spellchecking/linting.

[Gaurav0]

Looks good to me. @mansona ?

[mansona]

It seems like we are actually adding two things with this PR, one of which I would like to solve before we merge it.

a) adding the frail flag so remark will fail CI
b) implementing link checking (in a way that fails CI if it fails)

[mansona]

hey @maxwondercorn 👋

My point that I made on #77 (comment) was more along the lines of "if remark doesn't support it then maybe we can support it directly". I understand the benefits of having a command that we can run locally to check links but in a project that is 100% maintained by volunteers I know that we will have times where links sneak through, or indeed links break externally 🙈

I would prefer if we split this up into 2 PRs and kept the "external link checking" PR open until we had a solution that works in CI so that we don't silently assume that it's "done" because we merged the PR related to it.

I hope this all makes sense 😖

[maxwondercorn]

I understand the logic, so I'll close this pr and open a new one for error generation on lint fails.My goal it to have the checking done and anything that forces it is good.

You see something similar at work, a process that works until the current person(s) moves on and then it doesn't get done anymore... 😄