net/shmux: Update to 1.0.3

While I'm here:

• Switch to GitHub and update the WWW field to avoid redirects.
• Modernize the option knobs.
• Update the license that has changed with the new release.
• Add "localbase" to USES to fix a bug that has been there a long time if the PCRE option was enabled. Before that the configure script was able to find libpcre but used bogus paths for the -I and -L compiler flags which produced a binary that was never linked against libpcre.

PR: 238618
Submitted by: Thomas Merkel <tm@NetBSD.org>
Approved by: portmgr (blanket, unmaintained port)