Highlight the ? character for nullable type hints and return types

[fabacino]

I changed all the tests to expect the highlighting of the ? character to be the one of a data type.

Fixes #469

[ejmr]

@syohex

Feel free to add to the merge commit message:

Reviewed-by: Eric James Michael Ritz.

In the future I'll simply post the above Reviewed-by line for any patch I have downloaded and tested on my own computer.

[zonuexe]

@fabacino Thank you, I also checked the display in my environment.