Add shellfu template

bin/mkexec

         'ffoo'  => "\n. \"\$(ffoom path)\" || exit 3\n\n"
                    . "ffoo import pretty\n\n"
                    . "FFOO_DEBUG=true",
+        'shellfu'  => "\n. \"\$(shellfu-get path)\" || exit 3\n\n"
+                   . "shellfu import pretty\n\n"
+                   . "SHELLFU_DEBUG=\${SHELLFU_DEBUG:-true}\n\n"
+                   . "usage() {\n"
+                   . "    mkusage \"arg...\"\n"
+                   . "}\n\n"
+                   . "main() {\n"
+                   . "    while true; do case \$1 in\n"
+                   . "        -*) usage ;;\n"
+                   . "        *)  break ;;\n"
+                   . "    esac done\n"
+                   . "}\n\n"
+                   . "main \"@\"",
     },
 };