It was possible to pass some types of invalid UTF-8 through Jiffy's
encoder. Specifically, if uescaping isn't used, values that would decode
from 0xD800 to 0xDFFFF, 0xFFFE, 0xFFFF, and values greater than 0x10FFFF
would not be flagged as invalid. Now they are.
The encoder can now return \u escaped unicode data instead of leaving
it as UTF-8 byte sequences. This done like so:
Eshell V5.8.3 (abort with ^G)
1> jiffy:encode(<<240, 144, 129, 128>>, [uescape]).
<<"\"\\uD800\\uDC40\"">>