Fusion 360 Easel/Grbl post processor fix

The Grbl/Grbl post processor supplied by Autodesk and the Easel post processor (supplied by Inventables) which is derived from it both generate gcodes which are actually invalid for all versions of Grbl. The issues are:

The Tool Change M06 code is completely unsupported. The only reason this doesn’t cause the job to stop is the Gcode sender ignoring the error. Both the Grbl and Easel post processors generate this code and should simply delete it.

The generic Grbl processor adds a % at the beginning and end of the gcode - this is also not supported and should be removed.

The generic Grbl processor adds a M30 at the end of the file to turn off the spindle - the more correct code is M05.

I have opened a support forum topic in Autodesk’s forums to ask that these fixes are made. I believe that these fixes will solve a lot of problems experienced by X-Carve users when trying other Gcode senders, especially Picsender which does not ignore the errors they generate. If you would like to help encourage them to make this fix the topic is at https://forums.autodesk.com/t5/fusion-360-support/the-hsm-library-supplied-post-processor-for-grbl-includes-bad/td-p/8719294