Parametric Spindle Adapter

Parametric universal spindle adapter.

There are many other examples of this type of thing but this one is parametric. I found the rocking of the spool on extrude/retract cycles put a fair amount of tension on the filament and (at least before I put guides in place) could even snap it by pulling it at a high angle. Making the internal diameter of the spool closer to the diameter of the spool holder reduced the rocking significantly.

You might want to change the following values for your needs

`id` = internal diameter of the tube (must be larger than your spindle)
`od` = maximum external diameter of the ends (must be larger than the hole in your spool)
`length` = total end-to-end length (must be larger than the width of your spool)

If `nut` is true, it will print the nut. If `bolt` is true, it will print the bolt. If `nut` and `bolt` are both true, it will print both with 5mm between them on the x axis.

I haven't calibrated my printer fully, so I had to print the nut 2%