Include a way to select a capture zone with the cursor

[svenstaro]

Is your feature request related to a problem? Please describe.
You currently recommend using slop in a subshell like --size $(slop) for being able to select a capture zone. However, this is quite awkward and I'd really like for menyoki to just include that. It seems an odd omission in a tool such as this which comes with so many batteries just to find of them to be weirdly missing.

Describe the solution you'd like
Include a bunch of flags such as --size-select, --size-cursor, --size-window and don't depend on external tools for this.

Describe alternatives you've considered
A tool such as peek which has this.

Additional context
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