Add "enabled" and "severity"/"warning" to rule in Configuration object, add corresponding documentation and tests, update demo web app (fixes #254)”.

test/configure-file-with-severity-alias.md

@@ -0,0 +1,58 @@
+# Configure File With Severity Alias
+
+Text * text* {MD037}
+
+Text ` text` {MD038}
+
+Text [ text](.)
+
++ List item {MD004}
+
+Text (text)[.] {MD011}
+
+2. List item
+
+<!-- markdownlint-disable -->
+
+Text * text*
+
+Text ` text`
+
+Text [ text](.)
+
++ List item
+
+Text (text)[.]
+
+2. List item
+
+<!-- markdownlint-restore -->
+
+Text * text* {MD037}
+
+Text ` text` {MD038}
+
+Text [ text](.)
+
++ List item {MD004}
+
+Text (text)[.] {MD011}
+
+2. List item
+
+<!-- markdownlint-configure-file {
+  "default": false,
+  "no-space-in-emphasis": "error",
+  "no-space-in-code": "warning",
+  "no-space-in-links": false,
+  "ul-style": {
+    "severity": "error",
+    "style": "dash"
+  },
+  "no-reversed-links": {
+    "severity": "warning"
+  },
+  "ol-prefix": {
+    "enabled": false
+  }
+} -->