Support for additional metadata along with the download URL

[Sweetchuck]

Great tool. Looks like a usable alternative to PHIVE.

However I miss a few feature. (I know that this is a freshly published project.)

Checksum validation

Ability to add additional metadata to the download URL would open up the way to new features.

Similar to the cweagans/composer-patches 2.x

Current configuration format:

{
  "extra": {
    "remote-scripts": {
      "vendor/bin/foo": "<url>"
    }
  }
}

Proposed configuration format:

{
  "extra": {
    "remote-scripts": {
      "vendor/bin/foo": {
        "url": "<url>",
        "description": "optional",
        "checksum": "sha256:ugly-hash"
      }
    }
  }
}

Placeholder token for vendor/bin

The bin-dir directory can be configured.

{
  "config": {
    "bin-dir": "my-custom-bin"
  }
}

I think it would be easier (DRY) to use a variable for that in the destination path.

{
  "extra": {
    "remote-scripts": {
      "[bin-dir]/foo": {
        "url": "<url>"
      }
    }
  }
}