Dclab

- BREAKING CHANGE: Change np.meshgrid indexing in
`RTDCBase.get_kde_contour` from "xy" to "ij"
- feat: new submodule `kde_contours` for computing kernel density
contour lines at specific data percentiles (60)
- fix: range for contour KDE computation did not always contain end
value (`RTDCBase.get_kde_contour`)
- fix: `positions` keyword argument in `RTDCBase.get_kde_scatter`
was not correctly scaled in the logarithmic case
- ref: cleanup and document PolygonFilter.point_in_poly
- ref: move skimage code to separate submodule "external"
- ref: drop dependency on statsmodels and move relevant code
to submodule "external"

- fix: all-zero features were treated as non-existent due to relic
from pre-0.3.3 era
- fix: correct extraction of start time from tdms format
(1h offset from local time and measurement duration offset)
- fix: correct extraction of module composition from tdms format
(replace "+" with ",")
- enh: add configuration key mapping for tdms format to simplify
conversion to hdf5 format (see ``fmt_tdms.naming``)
- enh: do not add laser info for unused lasers for tdms format
- enh: dclab-verify-dataset checks for image attribute dtype
- enh: include original software version when exporting to rtdc format

- 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