Consolidate Markdown compatiblity into a single section

[mojavelinux]

Right now, it's a bit hard to find the syntax that is compatible with Markdown because it's spread out throughout the user manual. It might be more useful to have a section dedicated to this topic and then have the other sections in the user manual refer to it with an admonition block (TIP) when there's an alignment w/ Markdown.

[mojavelinux]

This section should also include an explanation about how AsciiDoc and Markdown are generally compatible with regards to basics such as:

• plain text markup
• paragraphs spaced by blank lines
• lists that with asterisks and dashes
• etc..

[jaredmorgs]

I'm going to do a search for all Markdown related content in the user guide and list it here to scope out the fix.

I think this first page is the best place to list the differences.

http://asciidoctor.org/docs/user-manual/#compared-to-markdown

Probably in a table with the following headings:

.Syntax Comparison Markdown | AsciiDoc | Comments

List the features in the following topics (some of which are placeholders for TODO content).

• http://asciidoctor.org/docs/user-manual/#sections (note about # headings)
• http://asciidoctor.org/docs/user-manual/#markdown-style-horizontal-rules
• http://asciidoctor.org/docs/user-manual/#markdown-style-blockquotes
• http://asciidoctor.org/docs/user-manual/#render-strings
• http://asciidoctor.org/docs/user-manual/#convert-markdown-strong-to-strong-asciidoctor

[mojavelinux]

That looks good.

Keep in mind this issue has two points of focus.

1. How AsciiDoc and Markdown compare (side-by-side as you suggested)
2. Additional Markdown compatibility that Asciidoctor provides