Parser.Markdown: Fix typo in type.
Added zero as return type on methods containing 'return 0'
Corrected types with zero
markdown: Allow replacement of the lexers and parser
markdown: Carry attributes from the lexer to the renderer
markdown: Add very basic autodoc markup to Renderer
markdown: Unprotect key classes to make them subclassable
markdown: Fix docs typos
Move Markdown into Parser and leave a stub behind in Tools