Add test on Curl\Handle object and complete Url::__toString behaviour when error

Signed-off-by: Stéphane HULARD <s.hulard@chstudio.fr>
Add documentation for magic methods and update ResponseFactory behaviour to use directly Handle instance

Signed-off-by: Stéphane HULARD <s.hulard@chstudio.fr>
Add test on Response and ResponseFactory objects and update coverage for their users.

Public now contains index.html instead of get.php to simplify urls

Signed-off-by: Stéphane HULARD <s.hulard@chstudio.fr>