Add a script to apply any config to any hunk in a config file.

[amtoine]

This PR adds the following features to the collection of scripts:

• let's say we'd like to automatically change the cava's config file to have new colors
• create a ~/.config/a2n-s/hunks.json config file
• put the following top level config for cava

  {
  "cava":
  {
  "file": "~/.config/cava/config",
  "hunks":
  {
    "palette":
    {
      "format": "{key} = '{value}'",
      "mapping":
      [
        "gradient_color_1:g1",
        "gradient_color_2:g2",
        "gradient_color_3:g3",
        "gradient_color_4:g4",
        "gradient_color_5:g5",
        "gradient_color_6:g6",
        "gradient_color_7:g7",
        "gradient_color_8:g8"
      ]
    }
  }
  }
  }

• then add #+ BEGIN:palette and #+ END:palette around the color gradient in ~/.config/cava/config like the following

  
  ...
  gradient_count = 8

+ BEGIN:palette

gradient_color_1 = '#d38578' gradient_color_2 = '#c6956c' gradient_color_3 = '#b9a560' gradient_color_4 = '#acb555' gradient_color_5 = '#9fc649' gradient_color_6 = '#92d63e' gradient_color_7 = '#85e632' gradient_color_8 = '#78f727'

+ END:palette

[smoothing] ...

- then run something like 
```bash
a2n-s-apply-to-hunks cava palette "g1:#ff9942 g2:#8a895b g3:#807974 g4:#77698d g5:#6d59a7 g6:#6449c0 g7:#5a39d9 g8:#f12af3"

[amtoine]

Let's add an example config file.