#82: regex-only escape not supported in re fallback module

[fireundubh]

Addressing #82:

• Reverted #46 regex-only changes to regular expressions
• Fixed issue where custom abbreviations test failed due to permission error

All current tests pass. Whether existing tests cover the Unicode issues that the regex-only \p escape was intended to address is another matter. The author of #46 should be able to provide insight into whether the existing tests cover those issues.

[brocksam]

Excellent work, @fireundubh, thank you!

The current tests do include examples with Unicode characters (#46 added the examples suggested in #33 where this was originally raised).

Play devil's advocate, would we be better off keeping the package's logic the same in the cases where regex is available and falling back to using re and the approach reimplemented in this PR if it is not? #46 and regex may well perform slightly different in edge cases that aren't in the current tests and if we keep the package functioning identically for instances where regex can be found then we don't risk breaking functionality for any downstream users.

I've added #84 which adds a simple GitHub Actions workflow to set up automated running of the tests using a configuration without regex and also a configuration with regex. Merging #84, in conjunction with this PR (#83), should help ensure that Titlecase continues to work with re as a fallback for regex going forward.

[brocksam]

This PR is now superseded by #84, with all credit to @fireundubh.

[ppannuto]

Closing in favor of #84.