Multiple api hosts

in response to ticket #44 

this pull request allows the following you to declare multiple api hosts in your config file

    apis: {
     "main": {
         host: "localhost",
         protocol: "http",
         port: "3022"
     },
      "api_one": {
          host: "fancyapi.foo.com",
          protocol: "https"
      },
      "api_two": {
          host: "fancyapi.bar.com",
          protocol: "http"
      }
    }

If you wish to use the 'main' api your model need only have a url and the rest will get picked up

    module.exports = Base.extend({
      url: '/users',
      idAttribute: 'id'
    });

will attempt to fetch data from `http://localhost:3022/users`

however, should you wish to use another api host your model may look more like the following

    module.exports = Base.extend({
      url: '/baz',
      idAttribute: 'id',
      apiHost: 'api_one'
    });

now, given the above snippets, the server will attempt to fetch data from `https://fancyapi.foo.com/baz`