Creates a new SharedIniFileCredentials object.

@param options [map] a set of options
@option options profile [String] (AWS_PROFILE env var or 'default')
the name of the profile to load.
@option options filename [String] ('~/.aws/credentials') the filename
to use when loading credentials.
function SharedIniFileCredentials(options) {
    AWS.Credentials.call(this);

    options = options || {};

    this.filename = options.filename;
    this.profile = options.profile || process.env.AWS_PROFILE || 'default';
    this.get(function() {});
  }