code: function create(callback, label) {
    if(!util.isFunction(callback)) {
      throw new Error('callback must be a function');
    }
  
    var resource = this.coinjar.personal.api_endpoint + '/v1/bitcoin_addresses.json',
        query = {};
  
    if(label) { query.label = label; }
  
    request.post(resource)
      .auth(this.coinjar.personal.auth_token)
      .send(query)
      .end(function (response) {
        if(isResponseError(response, callback)) { return; }
        return callback(null, response.body.bitcoin_address);
      });
  }
docs: @name create
  @description
  Create a new Bitcoin Address for user account.
  
  @params {Function} callback
  @params {String} label