Add composer configuration for packagist

[davidsneighbour]

To enable the framework as a PSR4 valid package for autoloading with composer require davidsneighbour/colossus-wp-options-framework#2.0.0-pre-001 I will add some configuration to the chore/repo branch and tag pre-releases in that branch.

something like the following:

  "autoload-dev": {
    "psr-4": {
      "Colossus\\Testing\\Browser\\": "tests/browser/",
      "Colossus\\Testing\\Unit\\": "tests/unit/"
    },
    "classmap": []
  },
  "autoload": {
    "psr-4": {
      "Colossus\\": "src/"
    }
  },

[davidsneighbour]

This is a breaking change because from now on the framework needs to be loaded via namespace like \Colossus\Classname