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/proselint/Spelling.yml

@@ -0,0 +1,17 @@
+extends: consistency
+message: "Inconsistent spelling of '%s'."
+level: error
+ignorecase: true
+either:
+  advisor: adviser
+  centre: center
+  colour: color
+  emphasise: emphasize
+  finalise: finalize
+  focussed: focused
+  labour: labor
+  learnt: learned
+  organise: organize
+  organised: organized
+  organising: organizing
+  recognise: recognize