0.1.3
 - add QPImage.raw_amp and QPImage.raw_pha
 - improve QPImage.__eq__
 - add "identifier":
   - meta data key
   - keyword for QPSeries.add_qpimage
   - property of and keyword for QPSeries
 - add convenience functions for item access in QPImage and QPSeries
 - moved to pathlib
 - minor API changes
0.1.2
 - allow strings and lists for `which_data` everywhere (#1)
 - check for valid background keys in image_data.py (#2)
 - add QPImage.info property (#5)
 - add slicing (#6)
 - add references to documentation (#7)
0.1.1
 - QPImage.set_bg_data now accepts QPImage objects
 - add QPSeries for managing multiple QPImages in one hdf5 file (#3) 
0.1.0
 - initial release
