Improving accuracy: magnifier, crosshairs, pixel values, resizable selection

[YodaEmbedding]

Features that can help users make reproducible, pixel-accurate screenshots:

• magnifier (near the mouse cursor, or perhaps on the cursor like hyprpicker)
• crosshairs
• pixel values indicator, e.g. (x, y) = (42, 666)
• resizable selection area after initial selection is made

maim --magnifier
maim --crosshairs
maim --pixel_indicator
maim --resizable_selection

Related: #281

[N-R-K]

resizable selection area after initial selection is made

This is already possible by pressing and holding down space. Also selection related issue should go to slop since that's what maim uses for selection.