added established content to user manual

- what is Asciidoctor
- Asciidoctor benefits
- what is AsciiDoc
- text editor
- installation instructions
- license
- authors
- ruby API and command line usage
- text formatting instructions and styles
- example block
- sidebar block
- comment block
- page break
- q and a block
- open block
- passthrough block
- optional delimiter section
- glossary
- ordered and unorder list basics
- labeled list
- hybrid list
- stylesheet factory section
- custom stylesheet section
- render to PDF
- render to DocBook 45
- render to deckjs
- intro to slideshows
- table column and cell sections
- substitutions and replacements
- removed old comments
- cleaned up links and link references
- fixed url summary table formatting