Update Digest to CPAN version 1.19

Update Digest to CPAN version 1.19

[DELTA]

1.19 Tue 2020-10-13
- Merge blead change: Remove . from @INC when loading optional modules.

1.18 Tue 2020-10-13
- Correct documentation for add_bits
- Explain $args,... in constructor prototypes
- Add base64_padded_digest method
- Add support for the SHA3 digests
- Update .gitignore and get make manifest working
- Github CI
- Move Digest to a more modern directory tree layout
- Enable strict/warnings for code and tests
- Drop use vars
- Provide a consistent tidy to the code base
- Get rid of the use of bareword file handles
- Modernize the changelog
- Use File::Temp for temporary test files