Enable vale for prose linting (#3)

* Enable vale in CI

* Add vale config

* Tweak vale

* Update config

* Update .gitignore

* Switch back

* Rename CI

* Add badges

* Tidy up CI

* Change image

* Configure vale

* Delint

* Update README

.github/styles/Readability/LIX.yml

@@ -0,0 +1,17 @@
+extends: metric
+message: "Try to keep the LIX score (%s) below 35."
+
+link: https://en.wikipedia.org/wiki/Lix_(readability_test)
+# Very Easy: 20 - 25
+#
+# Easy: 30 - 35
+#
+# Medium: 40 - 45
+#
+# Difficult: 50 - 55
+#
+# Very Difficult: 60+
+formula: |
+  (words / sentences) + ((long_words * 100) / words)
+
+condition: "> 35"