Enhancements
---------------
* Codebase is Python 3 now, keeping backwards compatibility to Python 2.7
via using the `future` module.
* min-max CML data can now be written to and read from cmlh5. Standard column
names are `tx_min`, `tx_max`, `rx_min` and `rx_max`. When reading from cmlh5
without specifying dedicated column names, the function tries out the
standard column names for min-max and instantaneous. If it does not find any
match it will print an error message.
* Added example file with min-max data for 75 CMLs. This dataset is derived
from the existing example dataset of 75 CMLs with instantaneous measurements.
* Added example notebook comparing min-max and instantaneous CML data
* Added TravisCI and Codecov and increased the test coverage a little
* Extended functionality for `append_data`. A maximum length or maximum
allowed age for the data can be specified
* More options for interpolation. Added option to pass `max_distance`
for IDW and Added option for resampling in `Interpolator`
(instead of just doing hourly means of variable `R`)
* Interpolated fields are now always transformed into an `xarray.Dataset`.
The `Dataset` is also stored as attribute if the `Interpolator` object
* Improved grid intersection calculation in validator
Bug fixes
---------
* `t_start` and `t_stop` have not been taken into account
in the main interpolation loop
* Fix: Catching `LinAlgError` in Kriging interpolation