Add simple ImageMagick wrapper scripts for quickly munging Luma3DS screenshots into shareable form

local/bin/luma-both-to-png

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+#!/bin/zsh
+date=${1%_*.bmp}
+magick ${date}_top.bmp ${date}_bot.bmp -alpha set -gravity Center -background 'rgba(0,0,0,0)' -append ${date}.png

local/bin/luma-to-png

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+#!/bin/zsh
+magick $f -alpha set -fill 'rgba(0,0,0,0)' -draw 'color 0,0 point' $f:r.png