multiple fixes for of_string functions

[hhugo]

• Z.of_string should accept string with a 0_ prefix.
• Q.of_string should not accept a sign after a dot (aka Q.of_string ".-0" should fail)
• Q.of_string should accept leading underscore after a dot, even if the integer part is empty (aka Q.of_string "._123" should succeed)

[hhugo]

This is ready for review

[hhugo]

@antoinemine, would you have time to review this PR ?

[antoinemine]

Does first_digit_after_dot works if the string ends with a dot?
Maybe find_in_string should return None when pos >= last, to be on the safe side.

[hhugo]

Does first_digit_after_dot works if the string ends with a dot?

I think it does

Maybe find_in_string should return None when pos >= last, to be on the safe side.

I've done that

[antoinemine]

OK. It seems good to me.

[hhugo]

Thanks
@antoinemine , How do you feel about a new release ?

[antoinemine]

There are still a couple of MR and issues we could look into before a release.

[hhugo]

I've opened #82 to track the new release and make sure we don't drop it by accident.