docs(router): fix markdown, and example mixin cleanup (#2101)

* docs(router): fix markdown and example mixin cleanup

- Fixed: markdown text not under `:marked` region (and so that text was
not showing up in the generated html).
- Fixed: code excerpt title `constructor` -> `isSelected`.
- Cleanup of all makeExample mixin uses.

This cleanup will help make it easier to record differences with the
deprecated router chapter (which must have app-relative makeExample
paths).

* post-review updates

Found another instance of markdown (a heading) outside of a `:marked` region.

Author: chalin

public/_includes/_util-fns.jade

@@ -98,14 +98,14 @@ mixin makeExample(_filePath, region, _title, stylePatterns)
 //- ending is given or is just (), then the title will be suffixed with
 //- either "(excerpt)", or "(#{_region})" when _region is defined.
 mixin makeExcerpt(_filePath, _region, _title, stylePatterns)
-  - var matches = _filePath.match(/(.*)\s+\(([\w ]*)\)$/);
+  - var matches = _filePath.match(/(.*)\s+\(([^\)]*)\)$/);
   - var parenText;
   - if (matches) { _filePath = matches[1]; parenText = matches[2]; }
   - var adjustments = adjustExamplePathAndTitle({filePath:_filePath, title:_title});
   - var filePath = adjustments.filePath;
   - var title = adjustments.title;
-  - var region = _region || parenText;
-  - var excerpt = !region || parenText === '' ? 'excerpt' : parenText || region;
+  - var region = _region || (_region === '' ? '' : parenText);
+  - var excerpt = parenText || region || 'excerpt';
   - if (title) title = title + ' (' + excerpt + ')';
   +makeExample(filePath, region, title, stylePatterns)(format='.')