Body map shapes

The muscle outlines in parts.json come from hugobonifay/body-map (commit 42957b15338ae6410c0e6a1380e062d4a50c10f3), which declares the MIT licence in its README. build-body-map.mjs redraws them for Coach Poulpy: it converts them to plain curves, keeps the shared muscle names, stretches the two builds, and leaves the skin transparent. Please keep this notice with the shapes.