Enable markdown-link-check (#1)

* Enable markdown-link-check

https://github.com/marketplace/actions/markdown-link-check

* Use markdown-link-check 1.0.14

To fix HTTP 503 errors I shouldn't be getting.

This change fixed it in three other repos:

- EliahKagan/userstyles#1
- EliahKagan/muntineer#2
- EliahKagan/fps#1

* Fix typo in referenced version tag name

* Try markdown-link-check 1.0.13

Moving from v1 to 1.0.14 fixed the wrong 503 errors, but gave many new errors for hash links (links to specific sections).

It's probably gaurav-nelson/github-action-markdown-link-check#127, in which case switching to 1.0.13 won't fix the hash link problem, but I want to try that before attempting to fix both problems at once by specifying branches or untagged commits.

* Try tip of master

For markdown-link-check.

* Back to v1

* Work around fussy links

.github/workflows/markdown-links-config.json

@@ -0,0 +1,8 @@
+{
+  "aliveStatusCodes": [200, 503],
+  "ignorePatterns": [
+    {
+      "pattern": "^http://www\.adobe\.com/$"
+    },
+  ]
+}

.github/workflows/markdown-links.yml

@@ -0,0 +1,19 @@
+name: Check Markdown links
+
+on:
+  push:
+    branches:
+      - master
+      - gh-pages
+  pull_request:
+  schedule:
+    - cron: '15 0,12 * * *'
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1
+      with:
+        config-file: .github/workflows/markdown-links-config.json