Add raw string/data support for Response::download

[lastguest]

Response::download now only accept a file/url, add support to raw string data.

Example :

Response::download([
  'filename' => 'test.csv',
  'mime' => 'text/csv',
  'body' => '..........',
]);

Using an array to pass raw data will not break retrocompatibility.

[gadiener]

Implemented. See commit 370c42d