Add "shared parser" class method to Wikitext::Parser
Add "shared parser" class method to Wikitext::Parser

This is probably a better place to keep the optional singleton instance
than in the String extension where it currently is.

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

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