Adds FleshKincaid and IELTS

.vale.ini

@@ -2,4 +2,4 @@ StylesPath = vale/styles
 MinAlertLevel = suggestion
 Packages = Google, proselint
 [*]
-BasedOnStyles = Vale, Google, proselint
+BasedOnStyles = Vale, Google, proselint, Readability

vale/styles/Readability/FleschKincaid.yml

@@ -0,0 +1,8 @@
+extends: metric
+message: "Try to keep the Flesch–Kincaid grade level (%s) below 8."
+link: https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests
+
+formula: |
+  (0.39 * (words / sentences)) + (11.8 * (syllables / words)) - 15.59
+
+condition: "> 8"

vale/styles/Readability/IELTS.yml

@@ -0,0 +1,13 @@
+extends: metric
+message: "Try to keep the IELTS-Inspired Readability Score (%s) within the range suitable for your target audience."
+link: https://www.ielts.org/about-the-test/how-ielts-is-scored
+
+# Hypothetical formula inspired by aspects of IELTS
+formula: |
+  (0.25 * (complex_words / words)) +
+  (0.25 * (long_words / words)) +
+  (0.25 * (syllables / words)) +
+  (0.25 * (words / sentences))
+
+# Adjust based on the desired complexity of your content
+condition: "> 7"

vale/styles/Readability/meta.json

@@ -0,0 +1,4 @@
+{
+  "feed": "https://github.com/errata-ai/Readability/releases.atom",
+  "vale_version": ">=2.13.0"
+}