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 think that by following the logic I can't see a case where it can be invalid but you are right. Better safe than sorry. Will add a check.