Improve parsing of Date input formats

[hanbings]

There are 10 time parsing formats mentioned in the GNU findutils manual: https://www.gnu.org/software/findutils/manual/html_node/find_html/Date-input-formats.html

Include:
General date syntax
Calendar date items
Time of day items
Time zone items
Combined date and time of day items
Day of week items
Relative items in date strings
Pure numbers in date strings
Seconds since the Epoch
Specifying time zone rules

However, we currently only support parsing of General date syntax.

[tertsdiepraam]

This probably fits what we're doing in the parse_datetime repository!

[hanbings]

cool! It seems so.
I would use it as a dependency to replace the existing parsing function. : )