Switch FILE an TEMPLATE arguments

With readline's C-., it's convenient to have the name of the new target
be always the last argument.

New syntax follows this convention and still makes the TEMPLATE optional
by using the plus sign as template name decorator.

The effect of the plus-sign use means that having some template names
already starting with plus would bring silly syntax with double-plus
sign.  Having two types of templates is not really all that meaningful
so let's solve that by merely removing `+` from the names and using it
merely in its decorator sense.

bin/mkx

 usage() {
     local self
     self="$(basename "$0")"
-    warn "usage: $self [-f|--force] FILE [[+]TEMPLATE]"
+    warn "usage: $self [-f|--force] [+TEMPLATE] FILE"
     warn "usage: $self -l|--list"
     exit 2
 }
     #
     # Print list of valid templates
     #
-    echo +pya
-    echo +shellfu
+    echo pya
+    echo shellfu
     echo Bash
     echo Lua
     echo Perl
 #shellcheck disable=SC2016
 mktemplate() {
     #
-    # Print template $1 for $FilePath
+    # Print template $Template for $FilePath
     #
-    # Template may be a name of built-in template (starting with
-    # plus sign) or language name (actually *interpreter* name).
-    #
-    local tmplname="${1:-$Template}"
-    case "$tmplname" in
+    case "$Template" in
         sh)
             echo "#!/bin/sh"
             echo ''
             echo "if __name__ == '__main__':"
             echo '    '
             ;;
-        +pya)
+        pya)
             echo '#!/usr/bin/python'
             echo '"""'
             echo 'A simple application'
             echo 'if __name__ == '__main__':'
             echo '    App.main(sys.argv)'
             ;;
-        +shellfu)
+        shellfu)
             echo "#!/bin/bash"
             echo ""
             echo '#shellcheck disable=SC1090'
             echo ''
             echo 'main "$@"'
             ;;
-        "")
-            mktemplate "$(guess_language)"
-            ;;
         *)
             die "unknown template or language: $Template"
             ;;
         -f|--force) careful=false; shift ;;
         -l|--list)  lstemplates; exit 0 ;;
         -*) usage ;;
+        +*) Template="${1:1}"; shift ;;
         *)  break ;;
     esac done
     FilePath="$1"
-    Template="$2"
     test -n "$FilePath" || usage
     test -f "$FilePath" && $careful && die "file already exists: $FilePath"
+    test -n "$Template" || Template=$(guess_language)
     mktemplate > "$FilePath"
     chmod +x "$FilePath"
 }