WIP: Save output diffraction intensities into .chi, .dat .gsas or .xye file formats.
DOC: modified the documentation in create_filepath
ENH: changed the function to _format_output_path

ENH: added check if the output file already exists and only blow it away if explicitly asked to

ENH: two functions one to validate the inputs and other to create a file path to save output intensities

ENH: changes according to the comments
TST: added the tests to save_output
API: removed due to api change

TST: modified the tests for save_output
STY: remove the extra spaces and checked with PEP8
BUG: now the code runs in both py2k and py3k has to add encode('utf-8') for the str in f.write()
DOC: Changed the documentation
API: save_output in save_powder_output.py is added to the skxray.io.api.py