Changes for PDL-DateTime distribution

0.004   2020/09/05
        - fix #1 + fix #2 (hangs when PDL::Complex is loaded)

0.003   2017/01/01
        - fix: dt_periodicity

0.002   2015/10/17
        - new methods: dt_year, dt_quarter, dt_month, dt_day

0.001   2015/10/16
        - initial version
