feat: use keyboard selection

[dadav]

I wanted to make a selection via keyboard and added this functionality. I also added some more options like:

• making the font color changeable (-L): The font-color used for writing the labels and dimensions.
• making label-selection font color changeable (-S): The font-color which is used when an area is selected.
• split the screen in rows/cols. (-m): Splits the outputs or the given restricted areas in rows/columns.
• show labels in rectangles (-l): Shows the label. The user can press a key and it will select the first match.
• set font size (-g): You can change the font size with this.
• add crosshair (-x): Used code from Crosshairs #95
• set crosshair color (-X): You can set the crosshair color with this.

This is an example how we could make use of this:

#!/bin/bash

# uses slurp to get x y and then clicks it

div=7

while [[ $div -gt 1 ]]; do
        if [[ -z $x ]]; then
                read -r x y w h < <(slurp -l -f "%x %y %w %h" -m "$div:$div")
        else
                read -r x y w h < <(<<<"$x,$y ${w}x${h}" slurp -l -f "%x %y %w %h" -m "$div:$div")
        fi

        div=$((div-2))
done

swaymsg seat - cursor set "$x" "$y"
swaymsg seat - cursor press button1
swaymsg seat - cursor release button1

And this is how I make use of this (first select the x, y coords and then use swaymsg to click it...like..what if someday the mouse is broken?)

foo.mp4

[tmccombs]

I left a few comments, but this PR also makes a lot of changes. Could it be split up into smaller pull requests so the changes could be reviewed in isolation?

[tmccombs]

This change would conflict with #138

[tmccombs]

Could we avoid allocating every time a key is pressed?

Couldn't we just use a char[1], since the only keyboard selectors we allow are single ascii characters, and should thus fit in a single byte? If the result doesn't fit in a single byte, then it isn't a key we care about.

[tmccombs]

Suggested change

	#define KEYBOAD_SELECTORS "abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	#define KEYBOARD_SELECTORS "abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ"

?