Allow initialization during tie

  New method: add
  Bump version to 1.900 trial
Update tests

  Test the add method
  Require Test::More 0.88
Require Perl 5.6.0

  Perl 5.6.0 is 14 years old now, drop compatibility with older versions
  Use warnings
  Use our instead of "use vars"
Indicate trial releases
Updated Changes for October 4, 2014 trial release of 1.900