~flexibeast/s6-portable-utils-man-pages

LICENSE: Update year range.
Use `MAN_DIR` in Makefile, instead of `MANPATH`.
Merge pull request #2 from capezotte/main

seekablepipe fixes:
* correct link in seekablepipe.1
* add seekablepipe.1 to Makefile
seekablepipe.1 fixes

Add to it to Makefile, and fix typo on upstream URL.
Initial commit.