Merge pull request #217 from ericdill/io_api

ENH : Implemented io api file
ENH: Added diffraction api test
MNT: Cleaned up tests and added api tests
Merge pull request #220 from ericdill/test_refactor

Test refactor
MNT: Fix python2-3 issue in read_binary

MNT: Try 2 on fixing sorting issue
Merge pull request #221 from ericdill/binary_fix

MNT: Fix python2-3 issue in read_binary
WIP: Save output diffraction intensities into .chi, .dat .gsas or .xye file formats.
STY: style fixed -PEP8
DOC: modified the documentation in create_filepath
ENH: changes after the comments, change  create_filepath to _valid_inputs
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 commits
ENH: changes according to the comments
TST: added the tests to save_output
API: removed due to api change
ENH: removed the save_gsas to create it in another PR
TST: modified the test for output_save

Conflicts:
	skxray/tests/test_io/test_powder_output.py
DOC: added a GSAS reader from GSAS-II