Log Message:
Update devel/libbson to 1.6.3.

libbson-1.6.3
- No change since 1.6.2; released to keep pace with libmongoc's
  version.

libbson-1.6.2
- This release further improves HP-UX compatibility, especially when
  building with CMake, and fixes some distribution issues we
  introduced when porting the documentation from Mallard to Sphinx.

Libbson-1.6.1
- This is a bugfix release that resolves GCC 7 compiler warnings,
  improves HP-UX compatibility, and avoids a test failure from
  launching too many threads on 32-bit MIPS.

Libbson-1.6.0
- Use jsonsl instead of libyajl as our JSON parsing library, parse
  JSON more strictly, fix minor parsing bugs.
- Extended JSON documents like '{"$code": "...", \ 
"$scope": {}}' are
  now parsed into BSON "code" elements.
- ISO8601 dates now allow years from 0000 to 9999 inclusive. Before,
  years before 1970 were prohibited.
- BSON floats and ints are now distinguished in JSON output.
- The library is now built and continuously tested with MinGW-W64 on
  Windows.
- The documentation is ported from Mallard XML to ReStructured Text,
  the HTML documentation is restyled, and numerous man page syntax
  errors fixed.
- All public functions now have the __cdecl calling convention on
  Windows.