ludic/changes/lab-png-16-bit.md

bump: patch type: feature ludic.lab: 16-bit PNGs — lab_png_write16_from(st, path, w, h, channels, px, at) writes 16-bit samples (two bytes each, most significant first) the way lab_png_write_from writes 8-bit ones, so a test can write a height map render3d's decoder reads back as R16; lp_png_bytes(stride, h) is the size of one.