webservices/json: update the JSON parser to version 1.1.0

json_parse_ex() now requires the length of the JSON string to parse.

The following changes are integrated:

• 672dd79c (int64 on Windows),
• ecb7c847 (proper include guards),
• c8edcab8 (null deref),
• 894bab1c (fallthrough warning)

The (unused) json_relaxed_commas flag is gone.

We may also use it as a contrib.