Consider switching to string streams instead of char streams

[aantron]

The performance will probably be much better, but compare and measure first.

[xguerin]

What is your intuition about this for performance improvement?

[aantron]

For consumers that allocate something per unit of output from the parser, giving them one byte at a time makes them allocate too much. Feeding them strings at a time (so chunks, basically) amortizes the cost of their allocations. Also, if they do unbuffered I/O, it saves overhead of doing system calls or other I/O one byte at a time, in the same way.

[xguerin]

Makes sense. I was looking at the code and since most of the internal logic is byte oriented, I was wondering whether or not it made sense to convert all functions to string streams. At this moment it is not clear to me that's the case. Especially if the original intent is I/O optimization, the outer API can expose string streams while some of the logic can retain its byte stream interface.

That being said, a benefit to more generally use strings instead of bytes would be to reduce the amount of continuation calls.