attribute selection options

[Michael Rossetti]

the citybikes network api endpoint offers "field filtering" (see description below), and as a user of this ruby library, I should be able to make those kinds of requests.

Fields can be filtered by adding a ?fields=list,of,fields parameter to any request. Field visibility gets only into the first document for now, but we plan on supporting lucene type parameters to allow filterings like location.city,station.* For example http://api.citybik.es/v2/networks?fields=id,name,href will render just the name, id and API endpoint of each network

{
  "networks": [
    {
        "href": "/v2/networks/velib", 
        "id": "velib", 
        "name": "V\u00e9lib'"
    }, 
    {
        "href": "/v2/networks/valenbisi", 
        "id": "valenbisi", 
        "name": "Valenbisi"
    }, 
    {
        "href": "/v2/networks/ecobici", 
        "id": "ecobici", 
        "name": "EcoBici"
    },
    {...}
  ]
}