0.8.2 (20230330)

- COPYING - Add copyrights for libslack's optional getopt/snprintf modules
- .reuse - Add copyrights for libslack's optional getopt/snprintf modules
- make - Exclude man-slack/html-slack/dist-slack from man/html/dist targets
- Fix libslack compile error and install error on Solaris
- doc - Replace http with https for libslack.org/raf.org and remove trailing /
- Change default compiler on OpenBSD to cc