Update to 4.12
    
    - New upstream release 4.12
      - Make encoder independent of Math::BigInt version (GH#140)
      - Rethrow error from eval_sv and eval_pv() (GH#138, GH#139), e.g. when
        Math::BigInt/BigFloat fails
      - Fix encoding Inf and NaN from PV and NV slots to JSON_TYPE_INT (GH#137)
      - Fix memory corruption in sv_to_ivuv() function (GH#136)
      - Add new method ->require_types (GH#135)
      - Fix typed json encoder conversion from scalar's PV and NV slot to
        JSON_TYPE_INT (GH#133, GH#134)
      - Fix inconsistency with warnings in typed json encoder (GH#131)
      - Fix Perl 5.8.0 support (GH#130)
      - Fixed minor pod typo (GH#129)
      - Document invalid recursive callbacks or overloads (GH#128)