Need to lowerCamelCase JSONPB key names

[j6carey]

According to the protobuf v3 specification:

Message field names are mapped to lowerCamelCase and become JSON object keys. If the json_name field option is specified, the specified value will be used as the key instead. Parsers accept both the lowerCamelCase name (or the one specified by the json_name option) and the original proto field name.

Current compile-proto-file keeps the original field name.

Note that testCase13 in tests/SimpleDecodeDotProto.hs would be able to decode from the JSONPB format emitted by Python if we were to add support for parsing lowerCamelCase conversions of field names.