Allow read_lines to gracefully skip null values

[nathanielng]

Unlike readLines(), readr::read_lines() doesn't have a skipNul=TRUE option. Hence it either chokes on null characters, or strings get truncated at the null character. Could a skipNul=TRUE option be implemented?

[hadley]

Is there some reason that even needs to be an option? Why shouldn't it always do so?

[nathanielng]

Come to think of it, I don't really see any need to be an option (even for backward compatibility). Perhaps Nuls should always be skipped, i.e. skipNul=TRUE always and skipNul=FALSE isn't allowed.

[hadley]

Can copy what CollectorCharacter::setValue() does