resolve #1 - add templates for AsciiDoc processing instructions

AsciiDoc inserts processing instructions into the generated DocBook. This patch adds XSL templates that handle those processing instructions consistence with the stylesheets in the AsciiDoc distribution.

- templates for AsciiDoc pis (line break, page break, rule)
- add asciidoc.mode to tune defaults when using AsciiDoc output
- set defaults for toc and numbered based on AsciiDoc pis when asciidoc.mode = 1
- fix inlinemediaimage to behave as an inline element