Update to 1.44
    
    - New upstream release 1.44
      - Sync test files with Math-BigInt-1.999707
      - Update the README file
      - Replace 'use vars ...' with 'our ...'; we require a Perl newer than 5.6.0
        anyway
      - Required version of Math-BigInt is now 1.999706
      - Add 'Test::More' to TEST_REQUIRES in Makefile.PL
      - Enable 'use warnings'; we require a Perl newer than 5.6.0 anyway
      - Add 'assertlib.*\.exe' to MANIFEST.SKIP, since make generates temporary
        files like 'assertlibzxjE4WfG.exe' on Cygwin