Solidity Natspec multiline /** .. */ comments

- Natspec now works with `/** ... */` type of comments.
- Some work on better formatting of the extracted text, especially on the multiline comments case
- Adding CR ('\r') as whitespace in the scanner
- Some tests
I have the impression that this can be simplified. I don't think we need to check `!m_source.isPastEndOfInput(1) && m_source.get(0) == '*' && m_source.get(1) == '/'` twice.