Adds default title (tooltip) of the example text unless overiden with "title" attribute
The "embedded-style" attribute causes link to open in new tab in the embedded style.
Use for samples that have a confusingly large number of files.
The "embedded" attribute option remains and displays _inline_ in the _same_ tab.
closes#1818
Previously, the markdown of some chapters was converted to Jade markup
to support the conditional exclusion of TS prose parts in Dart
chapters. This commit reverts some of that back to clean markdown,
thanks to a few custom directives.
