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/DateRedundancy.yml

@@ -0,0 +1,10 @@
+extends: existence
+message: "'a.m.' is always morning; 'p.m.' is always night."
+ignorecase: true
+level: error
+nonword: true
+tokens:
+  - '\d{1,2} ?a\.?m\.? in the morning'
+  - '\d{1,2} ?p\.?m\.? in the evening'
+  - '\d{1,2} ?p\.?m\.? at night'
+  - '\d{1,2} ?p\.?m\.? in the afternoon'