Update devel/libbson to 1.7.0.

- Changes to JSON encoding and decoding:
  - New functions bson_as_canonical_extended_json and
    bson_as_relaxed_extended_json convert BSON to canonical and
    relaxed extended JSON according to MongoDB Extended JSON Spec.
  - When parsing JSON type wrappers like "$timestamp", any missing or
    extra keys are an error.
  - The JSON format for BSON regular expressions is now
    "$regularExpression": {"pattern": "...", "options": "..."}.
  - The JSON format for BSON binary elements is now "$binary":
    {"base64": "...", "subType": "..."}.
  - BSON dates can be parsed from "$date" as an ISO8601 date or
    "$numberLong" as milliseconds since the epoch: "t": {"$date":
    {"$numberLong": "1234"}}.
  - The non-numbers NaN, Infinity, and -Infinity are now recognized
    (regardless of case) when parsing JSON.
- CMake build now installs .pc files for programs that link to libbson
  using pkg-config. Both the CMake and Autotools build systems now
  install .cmake
- New CMake option, "ENABLE_STATIC", defaults to ON.
- Minimum required CMake version has been increased to 3.1.
- New functions
  - bson_strcasecmp, a portable equivalent of strcasecmp.
  - bson_iter_as_double, cast the current value to double.
  - bson_iter_init_from_data, creates an iterator from BSON string.
  - bson_validate_with_error, checks a document like bson_validate
    does but also reports which key was invalid
- New convenience macros
  - BSON_ITER_HOLDS_INT, checks if iterator holds int32 or int64
  - BSON_ITER_HOLDS_NUMBER, checks if iterator holds int32, int64 or
    double
- Raised BSON recursion limit to 200


(fhajny)