Dtscalibration

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* Added reading support for zipped silixa files. Still rarely fails due to upstream bug.
* pretty __repr__
* Reworked double ended calibration procedure. Integrated differential attenuation outside of reference sections is now calculated seperately.
* New approach for estimation of Stokes variance. Not restricted to a decaying exponential
* Bug in averaging TMPF and TMPB to TMPW
* Modified residuals plot, especially useful for long fibers (Great work Bart!)
* Example notebooks updatred accordingly
* Bug in `to_netcdf` when passing encodings
* Better support for sections that are not related to a timeseries.

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* Double-ended weighted calibration procedure is rewritten so that the integrated differential attenuation outside of the reference sections is calculated seperately. Better memory usage and faster
* Other calibration routines cleaned up
* Official support for Python 3.7
* Coverage figures are now trustworthy
* String representation improved
* Include test for aligning double ended measurements
* Example for aligning double ended measurements

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* Many examples were shown in the documentation
* Fixed verbose settings of solvers
* Revised example notebooks
* Moved to 80 characters per line (PEP)
* More Python formatting using YAPF
* Use example of `plot_residuals_reference_sections` function in Stokes variance example notebook
* Support Python 3.7

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* Reworked the double-ended calibration routine and the routine for confidence intervals. The integrated differential attenuation is not zero at x=0 anymore.
* Verbose commands carpentry
* Bug fixed that would make the read_silixa routine crash if there are copies of the same file in the same folder
* Routine to read sensornet files. Only single-ended configurations supported for now. Anyone has double-ended measurements?
* Lazy calculation of the confidence intervals
* Bug solved. The x-coordinates where not calculated correctly. The bug only appeared for measurements along long cables.
* Example notebook of importing a timeseries. For example, importing measurments from an external temperature sensor for calibration.
* Updated documentation

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* No changes

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* New resample_datastore method (see basic usage notebook)
* New notebook on basic usage of DataStore
* Support for Silixa v4 (Windows xp based system) and Silixa v6 (Windows 7) measurement files
* The representation string now includes the sections
* Reorganized the IO related files
* CI: Add appveyor to continuesly test on Windows platform
* Auto load Silixa files to memory option, if size is small