tinyxxd 1.3.15

• Fix an issue with \r handling.
• Fix a padding bug in hex_littleendian.
• Performance improvements.
• Improve color handling, inspired by vim/vim@1578ea9, thanks @h-east.
• Respect the NO_COLOR environment variable.
• Use strtoll for xxd->length.
• Update CI configuration.
• Some refactoring / removing unused code / renaming variables.
• Add more tests.