Load 2 bytes and compare the 2 bytes against `"\u"`
Compilers with optimizations turned on will turn this into a 16-bit load
then 16-bit compare on supported platforms
(with smaller compiled code size).
Make it obvious to the compiler that it's reading two
consecutive bytes of the same pointer
Add parse_surrogate_pairs to show the difference exists.
See discussion in #1896
Tyson Andre
00564bf7d5