Update documentation for new options
Update documentation for new options

Add documentation for space_as_underscore and img_prefix.

Signed-off-by: Wincent Colaiuta <c76ac2e9cd86441713c7dfae92c451f3e6d17fdc@wincent.com>

geni/wikitext,geni/wikitext,barnaclebarnes/wikitext,geni/wikitext,wincent/wikitext,barnaclebarnes/wikitext,wincent/wikitext,barnaclebarnes/wikitext