Playscii 0.9.12

This is a minor release with a few small fixes:

- Fix to avoid a crash creating new document directories on Windows due to case-insensitivity.
- TXT export: use utf-8 encoding instead of allowing OS default which on (ANSI) Windows fails

This build also uses a much more recent build of Python (3.7) on Windows and macOS, and newer versions of various libraries. It should also not be incorrectly flagged as malware by Windows Defender; any future builds where you see this are random and I can't really do much about them other than create a new build with a few bytes changed, which seems to evade the rather aggressive signature detection that some antivirus suites use.