Parametric coffin stencil

A coffin shaped stencil.

Defaults to a "normal" coffin shape, which dynamically scales to match "head-to-foot length", including with non-default shape ratios.

Highly configurable:
- add internal crosshair supports
- interior fill (like a pool- don't confuse this with infill %)
- emboss with fully customizable text (requires interior fill for writing surface)

Note that default size is larger than most standard printer beds. Either scale it down to fit, or use your slicer of choice to split it into a multipart print.