Added the set_user_metadata() method that takes an object_id and optionally either listable and/or non-listable metadata in the form of a Python dictionary.  
Added the set_user_metadata() method that takes an object_id and optionally either listable and/or non-listable metadata in the form of a Python dictionary.  
lweeks/atmos-python,ab24v07/atmos-python,chadlung/atmos-python,MrBasset/atmos-python