Pcse

This release fixes a bug in the NASAPowerWeatherDataProvider which did not handle missing data properly. Some strange sentences in the installation section were fixed.

Last update before releasing PCSE 6.0. This release already includes all fixes to run PCSE on python3.

Main difference is a change in the assimilation routine where the 7-day running average TMIN is now calculated in the assimilation routine itself instead of in the engine. This has been done to avoid initialization problems causing to differences in the WOFOST model output depending on when you start on sowing or emergence.