Changed using module "mock" to "httpretty".

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Updated document.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Append option to pychecker.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>