added recursive flag to clone task, tests and documentation

Added an additional option to the gitclone task. The option is called **recursive**, and if set to a truey value, will add a ``--recursive`` argument to  the call to git clone.

The --recursive flag will instruct git to update and initialize all submodules in the cloned directory:
>>This is equivalent to running git submodule update --init --recursive immediately after the clone is finished 

Also added tests and documentation in README.md. Resolves #55.