Dclab

- 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]`

- feat: compute contours lazily (61)

- setup: migrate to PEP 517 (pyproject.toml)

- enh: ignore defective feature "aspect" from Shape-In 2.0.6 and 2.0.7
- enh: support loading HDF5 data using the 'with' statement
(e.g. `with dclab.new_dataset(rtdc_path) as ds:`)

- fix: add numpy build dependency (setup_requires)