Allow for dates that aren't necessarily in the yyyy-MM-dd format.

[dpsenner]

This reopens the old pull request 43. Please note that the old pull request 29 (reopened as #6) provides the same functionality.

[dpsenner]

With respect to #6 this patch is cleaner. Since this affects the current behavior and I have a bad feeling about changing the behavior of the rolling file appender, I see a unit test as a requirement for this pull request to proceed.

[fluffynuts]

Good day

It's been quite a while since this PR last saw activity. In an attempt to get pull requests under some semblance of
order, I'm having to make the uncomfortable decision to jettison pull requests which have been dormant for quite some
time. Perhaps arbitrarily, I'm choosing all pull requests which have not seen activity this year (2021), most of
which are marked as not building or have conflicts with the main branch.

This is not because the contributions aren't valuable - it's simply a matter of being the only person spending
some time on this and being a little overwhelmed. I'd rather get some traction on newer issues than continue
to try to understand, upgrade and work through PRs which don't build or which conflict with the main branch,
or which simply may have been solved in the mean time.

I encourage you to re-submit the PR against the current main branch if the issue is still significant. Your
contributions are appreciated. I apologise for any inconvenience caused and sincerely hope that you understand
the constraints involved which have brought me to the place of making this decision.