Death to htmlify! Overhaul of inline text parsing & substitutions

[mojavelinux]

This PR is a major step forward for Asciidoctor because it removes all remaining hardcoded HTML and opens the door for docbook output (all that remains is creating those templates). With the substitutions more organized, declarative configuration, extension & customization should fall right into place.

...and to add icing to the cake, it runs even faster than before.

Here's a summary of the modifications:

• inline text is rendered using templates
• create a common parent AbstractNode for all structured elements
• create a common parent AbstractBlock for section, block and list item
• create an Inline element for inline rendering
• correct quoted text substitutions to be fully compliant w/ AsciiDoc
• implement inline image macro
• implement inline passthrough macros (using extract & restore)
• add template for line break & callout
• add replacements substitution (for symbols like copyright, trademark, etc)
• substitute attributes in attribute values
• pull regexs for inline parsing into Asciidoctor module
• more robust regex for anchors and attribute lines
• double-line heading should not be allowed to start w/ a dot
• load tilt lazily (don't need to load if using built-in templates)
• remove import of unused cgi library
• optimized some regexs
• lots 'o tests
• more TomDoc

Happy New Year! 🎊

[erebor]

AH-mazing. 🚀

[mojavelinux]

Thanks Ryan! Thank you, too, for working with me throughout the holidays to keep things moving. It's been a great season. I look forward to what is to come in 2013! Cheers!