Add an attrGet method to Token

To make it easier to write code that consumes tokens for
tasks other than generating HTML.

lib/token.js

@@ -163,6 +163,20 @@ Token.prototype.attrSet = function attrSet(name, value) {
 };
 
 
+/**
+ * Token.attrGet(name)
+ *
+ * Get the value of attribute `name`, or null if it does not exist.
+ **/
+Token.prototype.attrGet = function attrGet(name) {
+  var idx = this.attrIndex(name), value = null;
+  if (idx >= 0) {
+    value = this.attrs[idx][1];
+  }
+  return value;
+};
+
+
 /**
  * Token.attrJoin(name, value)
  *

test/misc.js

@@ -357,4 +357,17 @@ describe('Token attributes', function () {
       '<pre><code class="bar"></code></pre>\n'
     );
   });
+
+  it('.attrGet', function () {
+    var md = markdownit();
+
+    var tokens = md.parse('```'),
+        t = tokens[0];
+
+    assert.strictEqual(t.attrGet('myattr'), null);
+
+    t.attrSet('myattr', 'myvalue');
+
+    assert.strictEqual(t.attrGet('myattr'), 'myvalue');
+  });
 });