Add README documentation for getVersion, leave promise/extendConfig undocumented (unsupported).

README.md

@@ -804,6 +804,31 @@ const results = lintSync({ "strings": { "content": original } });
 const fixed = applyFixes(original, results.content);
 ```
 
+### Miscellaneous
+
+To get the [semantic version][semver] of the library, the `getVersion` method
+can be used:
+
+```javascript
+/**
+ * Gets the (semantic) version of the library.
+ *
+ * @returns {string} SemVer string.
+ */
+function getVersion() { ... }
+```
+
+Invoking `getVersion` is simple:
+
+```javascript
+import { getVersion } from "markdownlint";
+
+// Displays the library version
+console.log(getVersion());
+```
+
+[semver]: https://semver.org
+
 ## Usage
 
 Invoke `lint` and use the `result` object's `toString` method:

example/standalone.mjs

@@ -1,10 +1,13 @@
 // @ts-check
 
-import { applyFixes } from "markdownlint";
+import { applyFixes, getVersion } from "markdownlint";
 import { lint as lintAsync } from "markdownlint/async";
 import { lint as lintPromise } from "markdownlint/promise";
 import { lint as lintSync } from "markdownlint/sync";
 
+// Displays the library version
+console.log(getVersion());
+
 const options = {
   "files": [ "good.md", "bad.md" ],
   "strings": {

test/markdownlint-test.mjs

@@ -692,6 +692,7 @@ test("readmeHeadings", (t) => new Promise((resolve) => {
           "#### callback",
           "#### result",
           "### Fixing",
+          "### Miscellaneous",
           "## Usage",
           "## Browser",
           "## Examples",