Use arguments to enable debug and verbosity in Shellfu template

bin/mkx

             echo ''
             echo 'shellfu import pretty'
             echo ''
-            echo 'PRETTY_DEBUG=${PRETTY_DEBUG:-true}'
-            echo ''
             echo 'usage() {'
             echo '    mkusage "arg..."'
             echo '}'
             echo ''
             echo 'main() {'
             echo '    while true; do case $1 in'
+            echo '        -d) PRETTY_DEBUG=true;   shift ;;'
+            echo '        -v) PRETTY_VERBOSE=true; shift ;;'
             echo '        -*) usage ;;'
             echo '        *)  break ;;'
             echo '    esac done'