Dclab

- feat: introduce user-defined plugin features (105)
- fix: dclab-verify-dataset now also prints other errors it encounters
- fix: installing the "lmer" R package failed, because "statmod" was not
installed
- fix: correct data types for "fluorescence:sample rate",
"imaging: roi position x", and "imaging: roi position y" (124)
- enh: support new .rtdc attribute "online_contour:bg empty" which is
True when the online background image is computed only from frames
that do not contain any events (124)
- enh: `AncillaryFeature` now populates other ancillary features when they
share the same method (104)
- enh: dclab-verify-dataset now returns a non-zero exit code if there
were errors, alerts, or violations (120)
- ref: streamlined dataset check function for missing meta data keys

- fix: add "chip identifier" to "setup" configuration section and
make it optional during dataset checks (109)
- fix: ignore empty metadata strings (partly 109); removed the
`check_metadata_empty_string` check function because it does
not apply anymore

- fix: some datasets with unknown feature names could not be
opened (AssertionError regression in 0.33.1)
- fix: workaround for sporadic JSONDecodeError when accessing DCOR
- ref: cleanup cli.py
- ref: cleanup util.py and deprecate `hash_class` argument in
`hashfile`

- fix: add dataset check for wrong medium written to .rtdc file
by Shape-In
- fix: filters were ignored when exporting trace data to hdf5 (112)
- enh: allow to set ICue identifier for integrity checking
- ref: code cleanup in export.py

- feat: introduce user-defined temporary features (point 2 in 98)
- fix: catch errors for integrity checks on non-raw datasets (102)
- fix: add check for negative fluorescence values (101)
- enh: add metadata keys for baseline offset (107)
- setup: remove deprecated setup.py test

- fix: add check for zero-flow rate in dclab-verify-dataset
- setup: added new file CREDITS for docs and only use maintainer
in setup.py
- docs: add autodoc to constant variables (94)
- docs: add "features_innate" and "features_loaded" to scripting
goodies section
- ref: cleanup of RTDCBase class
- ref: int/bool deprecation warnings in numpy 1.20.0 (93)
- tests: test for area_cvx as a float, consistent with output from
Shape-In (96)