minor, document %Z format specifier
Merge branch 'doc/format-specs'

* doc/format-specs:
  minor, document %Z format specifier
test, add regression case for anticommutativity of ddiff
fix, don't try and fix up negative remainders in precalc()
test, fix up dtdiff.025 result
Merge branch 'ddiff/anticommutativity'

* ddiff/anticommutativity:
  test, fix up dtdiff.025 result
  fix, don't try and fix up negative remainders in precalc()
  test, add regression case for anticommutativity of ddiff
test, provide regression tests for multiple sign bug in ddiff
doc, document behaviour of negative durations with multiple (refined) units

Only the largest unit will carry the minus sign.
fix, PEBKAC, actually provide a regression that matches the output
fix, in precalc() fix up refined units for negative durations
Merge branch 'bug/ddiff-multiple-negative-signs'

* bug/ddiff-multiple-negative-signs:
  fix, in precalc() fix up refined units for negative durations
  fix, PEBKAC, actually provide a regression that matches the output
  doc, document behaviour of negative durations with multiple (refined) units
  test, provide regression tests for multiple sign bug in ddiff
fix, don't try and fix up negative remainders in precalc(), part 2
Merge branch 'bug/ddiff-anticommutativity'

* bug/ddiff-anticommutativity:
  fix, don't try and fix up negative remainders in precalc(), part 2