Added composer.json so package can be managed by Composer

[khromov]

Added composer.json so this plugin can be installed and version managed by Composer.

More info:
http://composer.rarst.net/recipe/paths-control

Let me know if you have any questions!

[khromov]

Here is a complete example of how to use this with Composer:

composer.json

{
  "name": "my-project",
  "description": "",
  "license": "GPL",

  "repositories": [
    { "type": "vcs", "url": "git@github.com:lucasstark/acf-child-post-field.git" }
    ],

  "require": {
    "lucasstark/acf-child-post-field": "dev-master"
  },
  "extra": {
    "installer-paths": {
      "wordpress/wp-content/plugins/{$name}/": ["type:wordpress-plugin"]
    }
  }
}

@lucasstark If you register the package on https://packagist.org/ we can remove the VCS source:

composer.json

{
  "name": "my-project",
  "description": "",
  "license": "GPL",

  "require": {
    "lucasstark/acf-child-post-field": "dev-master"
  },
  "extra": {
    "installer-paths": {
      "wordpress/wp-content/plugins/{$name}/": ["type:wordpress-plugin"]
    }
  }
}

Branches can be chosen by using dev-BRANCH_NAME as the version. GitHub releases can be used as versions as well, more info:
https://getcomposer.org/doc/01-basic-usage.md#package-versions