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/Google/OptionalPlurals.yml

@@ -0,0 +1,12 @@
+extends: existence
+message: "Don't use plurals in parentheses such as in '%s'."
+link: "https://developers.google.com/style/plurals-parentheses"
+level: error
+nonword: true
+action:
+  name: edit
+  params:
+    - trim_right
+    - "(s)"
+tokens:
+  - '\b\w+\(s\)'