Detect and attempt to recover from json_encode errors triggered by
strings containing invalid UTF-8 sequences. Recovery will only be
attempted when encoding strings or arrays. If recovery fails then
a RuntimeException will be thrown.
The recovery process will convert invalid UTF-8 codepoints as though the
input string was encoded using the ISO-8859-15 character encoding. This
conversion may result in incorrect string output if the original
encoding was not ISO-8859-15, but it will be a valid UTF-8 string.
Closes#545
