ENH: Allow arbitrary date formats

[ludaavics]

When generating dates dynamically I've found it tedious to convert the objects to the required format.

• Added test cases with various date formats. All the tests pass with two exceptions, test_bulkref_two_ticker_one_field and test_bsrch. However, these tests currently fail in the main branch as well
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[matthewgilbert]

Thanks @ludaavics, will review when I get some free time.

[ludaavics]

hi @matthewgilbert -- just checking if you have any issue with the pr?

Thanks!

[matthewgilbert]

@ludaavics thanks for the PR. I reviewed it but I think a big change to the public facing API (even though this should be backwards compatible) is not something I want to introduce into the library at this point. I think this type of behaviour could be supported via decorators, so that is one option for supporting the behaviour in your own applications.