[enh] Adding the possibility to add feedstail.py to an other python project.
         * feedstail.py: renaming "loop" to "feedGenerator". feedGenerator will return a generator that returns an array. show will return a string.
         * config.py: Setting the config by kargs and remove "interval" and "oneshot" variables.
         * __init__.py: Correcting the import.
         * feedstail: Using the new version of feedstail.py and config.py.
[doc] adding a section about importing feedstail