0.4.3
 - fix: use memory address in QPImage.__repr__ if identifier not given
 - fix: only use meta.DATA_KEYS in QPImage.__eq__
 - cleanup: remove unused "dm exclude" meta.DATA_KEYS definition
0.4.2
 - fix: minor identifier ambiguity
0.4.1
 - docs: add example of mask-based correction with qpsphere
 - docs: minor cleanup
0.4.0
 - BREAKING CHANGE: replace all occurences of "binary"
   with "mask" to avoid ambiguities
0.3.0
 - feat: new meta data key "sim model"
0.2.1
 - ci: automate PyPI release with travis-ci
0.2.0
 - drop support for Python 3.5
 - docs: add QPSeries example to user API section
 - feat: `QPSeries.get_qpimage` supports QPImage identifier as index
 - feat: allow to set data storage dtype, which now defaults to float32
   to save disk space.
 - fix: set default gzip compression level to 9
 - ref: unify image data storage, set hdf5 chunks to image size
0.1.8
 - code cleanup
0.1.7
 - fix: bad default keyword argument in bg_estimate.estimate
0.1.6
 - implement qpimage refocusing function `QPImage.refocus`
 - API change: renamed "ramp" correction to "tilt" correction
 - add identifier to represenation string in QPImage
 - hologram analysis:
   - add disk, square, and tukey filters
   - standard "gauss" filter is replaced by "disk" filter 
   - standard filter size is set to one third of the distance
     between the sideband and the central band
   - allow to set hologram-retrieval parameters as a keyword
     argument "holo_kw" in QPImage
0.1.5
 - support nan values in phase data
 - add fletcher32 checksums and gzip compression to hdf5 files (#10)
 - allow to hard-link background-correction data in QPSeries
0.1.4
 - more __init__ checks for QPImage and QPSeries (user convenience)
 - allow negative indices in QPSeries.get_qpimage
 - Bugfix: `bg_estimate` does not compute intersection but union (#9)
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
