Set footnote extension's parser to Markdown's instance of the parser rather than giving it its own. Now footnote defs will parse the same (if another extension modifies the parser). Also updated and added doc strings.
Set footnote extension's parser to Markdown's instance of the parser rather than giving it its own. Now footnote defs will parse the same (if another extension modifies the parser). Also updated and added doc strings.

joachimneu/Python-Markdown,zestedesavoir/Python-ZMarkdown,cyisfor/Python-Markdown,joachimneu/Python-Markdown,dataquestio/Python-Markdown,craigds/python-markdown,evertqin/Python-Markdown,fernandezcuesta/Python-Markdown,waylan/Python-Markdown,fernandezcuesta/Python-Markdown,gogobook/Python-Markdown,evertqin/Python-Markdown,me-and/Python-Markdown,me-and/Python-Markdown,waylan/Python-Markdown,dataquestio/Python-Markdown,gogobook/Python-Markdown,gogobook/Python-Markdown,joachimneu/Python-Markdown,dataquestio/Python-Markdown,cyisfor/Python-Markdown,evertqin/Python-Markdown,fernandezcuesta/Python-Markdown,zestedesavoir/Python-ZMarkdown,cyisfor/Python-Markdown,Situphen/Python-ZMarkdown,Situphen/Python-ZMarkdown,zestedesavoir/Python-ZMarkdown,me-and/Python-Markdown,Situphen/Python-ZMarkdown