TECH-1087: Allow building to same directory - #678

To use it in prelude, you'd update package.json...

  "dependencies": {
    "kalastatic": "github:kalamuna/kalastatic#same-dir-dest",
    "sass": "1.89.2"
  },

  "kalastatic": {
    "source": "styleguide",
    "destination": "styleguide",
    "debug": "true",

This works for my particular case, but to make it more general purpose we might want to consider something like an actual cleanup setting with values for "all", "html", and "none".

Let me think about it a bit more.