audio/shoutcast: Significant overhaul of Makefile and cleanup.

• Bump PORTREVISION
• Fix *_DESC variable for SERVERSETUP option
• Simplify post-patch
• Remove unneeded mkdir, if sub-directories available for creation
• Silence mkdir
• Use COPYTREE_SHARE with directory/file patterns, instead of manual copying of each file
• Remove pkg-plist and use dynamic package list with PORTDATA, PORTDOCS, PORTEXAMPLES, PLIST_FILES and PLIST_DIRS
• Fix unexec usage, because it was deprecated

PR: 210203
Submitted by: lightside@gmx.com