Better half-markdown.
This fixes some issues with the current semi-markdown-parser to make life easier until a full markdown parser is implemented.
Changes:
- A * that would normally start italics but isn't matched by a closing *, is now left alone.
- A ` that would normally start a code block but isn't matched by a closing `, is now left alone.
- Backslashes should work as expected.
- Support for **bold** and the alternative _italic_ style.