Dclab

- feat: add new feature: gravitational force, temperature,
and ambient temperature
- ref: remove unused `has_key` function in
`rtdc_dataset.config.CaseInsensitiveDict`
- setup: require numpy>=1.10.0 because of `equal_nan` argument in `allclose`

- fix: usage of "xor" (^) instead of "or" (|) in statistics
- feat: support `remove_invalid=False` in downsampling.downsample_rand (27)
- feat: add keyword arguments `xscale` and `yscale` to improve data
visualization in `RTDCBase.get_downsampled_scatter`,
`RTDCBase.get_kde_contour`, and `RTDCBase.get_kde_scatter` (55)
- enh: make downsampling code more transparent
- BREAKING CHANGE: low-level downsampling methods refactored
- downsampling.downsample_grid: removed keyword argument
`remove_invalid`, because setting it to `False` makes no sense
in this context
- downsampling.downsample_rand: changed default value of `remove_invalid`
to `False`, because this is more objective
- rename keyword argument `retidx` to `ret_idx`
- these changes do not affect any other higher level functionalities
in `dclab.rtdc_dataset` or in Shape-Out

- feat: add new ancillary feature: principal inertia ratio (46)
- feat: add new ancillary feature: absolute tilt (53)
- feat: add computation of viscosity for water (52)

- fix: channel width not correctly identified for old tdms files

- ci: automate release to PyPI with appveyor and travis-ci

- fix: image export as .avi did not have option to use unfiltered data
- fix: avoid a few unicode gotchas
- feat: use Doane's formula for kernel density estimator defaults (42)
- docs: usage examples, advanced scripting, and code reference update (49)