Flexible time description

[chillenzer]

In working through #56, we found that the reasonable looking format YYYY-MM-DD HH:MM is not supported. Maybe we should have a more flexible format to make the process of contributing more robust and accessible. I could envision a few routes:

• Add support for parsing more general time stamps. This would be somewhat more user-friendly but would also have some drawbacks like:
  • Wrong/unintuitive defaults
  • Inconsistent data formats in _data/main.yaml
• Github action automatically standardizes the format during creation of the PR. That would make the data format consistent but could still result in wrong defaults being applied.
• On failed parsing, the Github action reports some human-readable error message to the committer (in PR or issue).

The latter is kind of what currently happens by hand, so don't know if that would need automation (as long as you can handle it by hand likely not).

[Sparrow0hawk]

I've started to address this in #83 with more flexible time stamp parsing using python-dateutil. I will try and have a look at getting better messages from the GitHub action too.