dateutils v0.3.1 released

[hroptatyr]

This is a bugfix release.

Bugfixes:
- octave/matlab code is distributed fully
- negative durations with refined units are minus-signed only once
- ddiff is entirely anticommutative now
- tests don't fail if zones don't exist on the build system
- dseq with empty ranges will no longer produce output (just as seq(1))
- arbitrary integers are not interpreted as time anymore
- when converting from zone info properly clear zone difference for %Z
- dseq(1) will automatically resort to +1mo and +1y iterators for
  wildcarded ymd dates
- dadd(1)'ing ywd dates with output as ymd works properly now

Features:
- ddiff can output nanosecond diffs
- automatic fix-up of dates is documented now
- parser errors and fix ups are reported through return code 2
- dseq with no `-f|--format` stays in the calendric system of the start
  value instead of converting all output to ymd