Numerous configuration and syntax enhancements

[mojavelinux]

Summary of changes:

• Reworked the convert.sh script to allow the formats to be specified (defaults to html,docbook,fopdf)
• Configured image paths so previews work when viewing / rendering an individual chapter
• Put the UI macros to use (keybinding, button and menu) (requires setting the experimental attribute)
• Demo the use of open block as a content container (like a div) to simplify lists with complex content
• Remove unnecessary option="header" attribute on tables (Asciidoctor works it out by convention)
• Configure syntax highlighting
• Additional minor cleanups, grammar and spelling corrections

Best practices regarding images:

• You should not hardcode the path to the image. Instead, the image path should be relative to the "image catalog", which can be configured on a per-document or per-build basis.
• Titles for block (standalone) images should be specified above the macro

[mojavelinux]

The imagesdir assignment is necessary for previewing the document on GitHub or when rendering the chapter individually. This value is overridden by the convert.sh script.

[arun-gupta]

This is really a great pull request and cleans up asciidoc and much better rendering.

Can we have the headers in a single line instead of spanning multiple ?

[mojavelinux]

Thanks Arun! Hopefully you can pick up on some of the suggestions and apply them throughout the lab. When I have more time I'd be glad to continue to refine the syntax as well.

To which headers are you referring?

[arun-gupta]

Yes, I'll apply the suggestions through out the lab and hopefully be able to author better asciidoc documents.

Page headers ?