Inline parsers are now defined as a list of delegates created according to the settings.
This is needed so that in future extensions such as `~~foo~~` can be implemented more easily.
Strangely enough, performance is not affected by this change.
Added strikethrough parser (`~~foo~~` -> `<del>foo</del>`). Disabled by default, can be enabled through settings.
Refactored unit tests (duplicate code removal).
Fixed parsing of empty ordered list item if it was not followed by a space.
See https://github.com/jgm/CommonMark/issues/242
Fixed nested link parser. See https://github.com/jgm/CommonMark/issues/252