Improved handling of extended M commands (plugin based) command words.

Fixes issues for programs containing extended M-codes using single meaning words (which they as a rule should not do).
Added core support for spindle encoder binding to spindles.
Added sorting of spindle report: enabled spindles are sorted first in order of spindle number, disabled by type then spindle id.
Changed realtime report to report spindle number instead of spindle id on changes in the |S: element.

report.h

@@ -52,6 +52,8 @@ void report_warning (void *message);
 // Prints Grbl help.
 status_code_t report_help (char *args);
 
+void report_plugin (const char *name, const char *version);
+
 // Prints Grbl settings
 void report_grbl_settings (bool all, void *data);