Add composer file

[strarsis]

@johngodley: This PR adds a composer.json file and adjust gitignore (vendor/).

Before merging, please verify and/or adjust the author email address
(wasn't able to find one) and whether license is GPL3-only or GPL-3.0+.

Closes #623.

This also allows to install beta versions of redirection plugin from GitHub using composer.

[strarsis]

Notice: Currently I am using this addition to composer.json for
installing without composer.json in plugin repository:

  "repositories": [
    {
      "type": "package",
      "package": {
        "name": "johngodley/redirection",
        "type": "wordpress-plugin",
        "version": "3.1",
        "source": {
          "url": "https://github.com/johngodley/redirection",
          "type": "git",
          "reference": "master"
        }
      }
    }
  ],
  "require": {
    "johngodley/redirection": "*"
  }

[johngodley]

Thanks!

I'm not that familiar with composer. Does this live in the zipped plugin on wordpress.org, or just here on github? If it's just here on Github it probably means it will pull down a lot of the build files that don't need to be on a live site - is there a way to ignore those?

[strarsis]

@johngodley: Currently it seems that all files are pulled by composer.
Similar/related composer issue: composer/composer#1750

[vinkla]

If it's just here on Github it probably means it will pull down a lot of the build files that don't need to be on a live site - is there a way to ignore those?

This is possible with the .gitattributes file. Basically a list of files to ignore.

---

Side note; since this plugin is published to wordpress.org users of Composer can install it with WPackagist.

[strarsis]

@vinkla: Right, but in this particular case I wanted to install it directly from GitHub master because of a fix I wanted to apply without waiting for the next release to the WordPress plugin directory.