Geonum

What's Changed
* Fixes related to pyplis library by jgliss in https://github.com/jgliss/geonum/pull/47


**Full Changelog**: https://github.com/jgliss/geonum/compare/v1.5.1...1.6.0

**Full Changelog**: https://github.com/jgliss/geonum/compare/v1.5.0...v1.5.1

New Contributors
* jgliss made their first contribution in https://github.com/jgliss/geonum/pull/7
* magnusuMET made their first contribution in https://github.com/jgliss/geonum/pull/24

**Full Changelog**: https://github.com/jgliss/geonum/compare/v1.4.4...v1.5.0

Bug fixed in `atmosphere` module, in method `density`, that gave wrong results when providing a temperature. Everything else is as in v1.4.3.

geonum is now tested for Pyhton 2.7 and 3.6 on OSX, Windows and linux and can be installed via:

conda install -c conda-forge geonum

Compared to the last release (v1.4.1), this release mainly comprises a code cleanup related to matplotlib imports in the individual modules, to simplify CI/CD for distribution via conda-forge. No changes to the geonum source code were applied.

This release mainly comprises more tests and updated installation and dist settings, for deploying via conda-forge. No changes in geonum source code.