ci: setup docs prose linting with vale

- only deploy if prose lint passes
- rework styles download
- add vale anotations matcher
- set MinAlertLevel to warning
- add website pages to the prose linter
- do not fail on docs linting

.github/vale/styles/.gitignore

@@ -0,0 +1,4 @@
+*
+!Makefile
+!LibreTime
+!Vocab

.github/vale/styles/LibreTime/NameCasing.yml

@@ -0,0 +1,6 @@
+extends: substitution
+message: Consider using '%s'
+level: warning
+ignorecase: false
+swap:
+  Libretime: LibreTime

.github/vale/styles/Makefile

@@ -0,0 +1,18 @@
+.PHONY: all
+
+SHELL = bash
+
+%.zip:
+	wget -q $(URL) -O $@
+
+Google.zip: URL=https://github.com/errata-ai/Google/releases/latest/download/Google.zip
+Microsoft.zip: URL=https://github.com/errata-ai/Microsoft/releases/latest/download/Microsoft.zip
+
+%: %.zip
+	unzip -qq $<
+	touch $@
+
+STYLES := ./Microsoft ./Google
+STYLES_ZIP := $(addsuffix .zip,$(STYLES))
+
+all: $(STYLES)