add screenshot scripts

scripts/screenshot-active-to-clipboard.sh

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+#!/bin/sh
+maim --select -u 
+

scripts/screenshot-to-clipboard.sh

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+#!/bin/sh
+maim --select -u | xclip -selection clipboard -target 'image/png'

scripts/screenshot-to-file.sh

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+#!/bin/sh
+maim --select -u ~/$(date +%s).png