Ref Guide: support Bootstrap components like tabs and pills

The theme I initially copied as the basis for the new Ref Guide included a Bootstrap integration, which has the potential to provide us with a number of options, such as organizing some content on a page into tabs (to present the same information in multiple ways - such as Windows vs Unix commands, or hand-editing schema.xml/managed-schema vs Schema API examples).

However, the way AsciiDoctor content is inserted into a Jekyll template made it difficult to know how to use some of Bootstrap's features. Particularly since we have to make sure whatever we put into the content comes out right in the PDF.

I had a bit of a breakthrough on this, and feel confident we can make straightforward instructions for anyone who might want to add this feature to their content. A patch will follow shortly with more details but the summary is:

• Add an AsciiDoctor passthrough block that includes the Bootstrap HTML code to create the tabs.
  • This has an ifdef::backend-html5[] rule on it, so it will only be used if the output format is HTML. The PDF will ignore this section entirely.
• Use AsciiDoctor's "role" support to name the proper class names, which AsciiDoctor will convert into the right <div> elements in the HTML.
  • These will take multiple class names and a section ID, which is perfect for our needs.
  • One caveat is the divs need to be properly nested, and must be defined on blocks so all the content is inserted into the tab boxes appropriately. This gets a little complicated because you can't nest blocks of the same type (yet), but I found two block types we aren't using otherwise.
  • The PDF similarly ignores these classes and IDs because it doesn't know what to do with custom classes (but in the future these may be supported and we could define these in a special way if we want).
• Modify some of the CSS to display the way we want since AsciiDoctor inserts some of its own classes between the defined classes and the inheritance needs to be set up right. Also the default styling for the blocks needs to be changed so it doesn't look strange.

I'll include a patch with a sample file that has this working, plus detailed instructions in the metadocs. In the meantime, I've attached a screenshot that shows a small snippet from my testing.

While the focus here is using tabs & pills, we will be able to use the same principles to support collapsing sections if that's preferred for presentation.