- Add HEIM_JSON_F_ESCAPE_NON_ASCII to indicate that non-ASCII must be
escaped as \uXXXX.
- Add HEIM_JSON_F_NO_ESCAPE_NON_ASCII to force non-escaping of BMP
codepoints.
- If the locale's codeset is not UTF-8 and
HEIM_JSON_F_NO_ESCAPE_NON_ASCII is not set, then set
HEIM_JSON_F_ESCAPE_NON_ASCII.
- Add flags for indenting with 2, 4, or 8 spaces, still defaulting to
tabs if none of those are set.
- Don't emit a newline before emitting scalar values in dicts.