commonmark-java 0.4.0

Update to CommonMark spec 0.24 (#28):

• No longer allow whitespace between link text and link label
• Don't allow whitespace in link destination even with <>
• Don't use whitelist for schemes in autolinks, recognize all 2-32 length schemes (see spec)
• Allow multi-line content in setext headings

API breaking changes (caused by changes in spec):

• Rename Header to Heading
• Rename HorizontalRule to ThematicBreak
• Rename HtmlTag to HtmlInline
• Replace MatchedBlockParser#getParagraphStartLine with #getParagraphContent that returns the current content if the the matched block is a paragraph