* Removed generic snapmaker machine and toolhead configuration. The idea of running a CNC code that is not matched to the machine's abilities and work area seems dangerous.
* --machine argument is required
* --toolhead argument is required when the selected machine is compatible with more than one toolhead. When the selected machine only supports one toolhead, it is selected as the default.
* --spindle-percent defaults according to the selected toolhead capabilities. If the toolhead can do RPM, then RPM is used, otherwise falls back to percent. This option now functions as an override.
* fixed a bug in convert_spindle() when RPM is selected. The gcode was not returned.
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