libsmartcol docs: Format samples, lists, tables

libsmartcol docs: Format samples, lists, tables

Use gtk-doc constructs to mark up formatted sections of documentation
so that they display properly in the rendered output.

- Enclose code samples with informalexample+programlisting tags
- Enclose preformatted blocks of text (tables) in same
- Present numbered lists in markdown format (leading 1., 2., etc.)
  so that they're translated into HTML ordered lists

Signed-off-by: FeRD (Frank Dana) <ferdnyc@gmail.com>