Dclab

- ref: convert said ValueError to ContourIndexingError

- fix: ValueError when verifying contour frame index due to comparison
of float with int

- feat: new command line script for creating a scalar-feature-only
dataset with all available ancillary features "dclab-condense"
- enh: enable scalar feature compression for hdf5 export
- docs: fix doc string for dclab-tdms2rtdc
(`--include-initial-empty-image` falsely shown as "enabled by default")

- feat: allow to obtain a mask representing the filtered data with
the `ret_mask` kwarg in `RTDCBase.get_downsampled_scatter`
- feat: allow to force-exclude invalid (inf/nan) events when downsampling
using the `remove_invalid` keyword argument
- feat: exclude empty initial images in dclab-tdms2rtdc;
they may optionally be included with "--include-initial-empty-image"
- feat: new property `RTDCBase.features_innate` (measuerd feature)
- enh: log which ancillary features were computed in dclab-tdms2rtdc (65)
- enh: improved tdms meta data import (also affects dclab-tdms2rtdc)
- enh: update channel count and samples per event when writing hdf5 data
- enh: dclab-verify-dataset now recognizes invalid tdms data
- enh: several other improvements when reading tdms data
- enh: group meta data in log files (dclab-tdms2rtdc and dclab-join)
- fix: correctly handle hdf5 export when the image or contour columns
have incorrect sizes (affects dclab-tdms2rtdc)
- fix: ignore empty configuration values when loading tdms data
- fix: image/contour files were searched recursively instead of
only in the directory of the tdms file
- fix: check for precence of "time" feature before using it to
correct measurement date and time
- fix: ancillary feature computation for brightness had wrong
dependency coded (contour instead of mask)
- fix: ancillary feature computation when contour data is involved lead to
error, because `LazyContourList` did not implement `identifier` (see 61)
- ref: remove NoContourDataWarning for tdms file format
- tests: improve dataset checks (64)

- feat: add command line script for joining measurements "dclab-join" (57)
- feat: make log files available as `RTDCBase.logs`
- feat: include log data in "dclab-join" and "dclab-tdms2rtdc"
- fix: `features` property for tdms file format falsely contains
the keys "contour", "image", "mask", and "trace" when they are
actually not available.
- enh: support loading TDMS data using the 'with' statement
- docs: add example for joining measurements
- docs: other minor improvements
- setup: add Python 3.7 wheels for Windows (62)
- setup: remove Python 2 wheels for macOS

- docs: add example for fluorescence trace visualization
- docs: restructure advanced usage section
- ref: make dclab in principle compatible with imageio>=2.5.0;
Dependencies are pinned due to segfaults during testing
- setup: make tdms format support and data export dependency optional;
To get the previous behavior, use `pip install dclab[all]`