fix(anchors): use entire heading text for auto named anchors

Auto-named anchors used only last _text_ token of heading.
I fixed that, and now auto-naming is generated from contents of all _text_ tokens of heading.

Also, it fixed some cases where inline markup got into auto-generated anchors and they became broken

_Example markup_: `## _Lorem ~~ipsum **dolor** sit~~ amet_`
__Before__: auto anchor is `#amet`
__Now__: auto anchor is `#lorem-ipsum-dolor-sit-amet`

src/transform/utils.ts

@@ -50,20 +50,20 @@ export function headingInfo(tokens: Token[], idx: number) {
     const openToken = tokens[idx];
     const inlineToken = tokens[idx + 1];
 
-    let lastTextToken,
+    let title = '',
         i = 0;
     while (inlineToken.children && i < inlineToken.children.length) {
         const token = inlineToken.children[i];
 
         if (token.type === 'text') {
-            lastTextToken = token;
+            title += token.content;
         }
 
         i++;
     }
 
     const level = Number.parseInt(openToken.tag.slice(1), 10);
-    const title = (lastTextToken && lastTextToken.content) || inlineToken.content;
+    title ||= inlineToken.content;
 
     return {
         level,

test/anchors.test.ts

@@ -118,4 +118,14 @@ describe('Anchors', () => {
                 '<p>After include</p>\n',
         );
     });
+
+    it('should add anchor with auto naming, using entire heading text', () => {
+        expect(transformYfm('## _Lorem ~~ipsum **dolor** sit~~ amet_\n\nParagraph\n')).toBe(
+            '<h2 id="lorem-ipsum-dolor-sit-amet">' +
+                '<a href="#lorem-ipsum-dolor-sit-amet" class="yfm-anchor" aria-hidden="true">' +
+                '<span class="visually-hidden">Lorem ipsum dolor sit amet</span></a>' +
+                '<em>Lorem <s>ipsum <strong>dolor</strong> sit</s> amet</em></h2>\n' +
+                '<p>Paragraph</p>\n',
+        );
+    });
 });