composer.json

{
    "name": "calderawp/twitter-thing",
    "description": "POC for a twitter plugin",
    "type" : "wordpress-plugin",
    "require": {
        "abraham/twitteroauth": "dev-master",
        "calderawp/tweet_core": "dev-master"
    },
    "license": "gpl",
    "authors": [
        {
            "name": "Josh Pollock",
            "email": "Josh@CalderaWP.com"
        }
    ],
    "minimum-stability": "dev",
    "autoload": {
      "psr-4": {"calderawp\\twitter_thing\\": "src/"}
    }
}

plugin.php

<?php
/*
 Plugin Name: Twitter Thing
 */
add_action( 'init', function(){
	include_once( dirname( __FILE__ ) . '/vendor/autoload.php' );

	new calderawp\twitter_core\core();

});