6.4.0

HydPy 6.4 includes two relevant changes:

1. It is now possible to store additional files (README, .gitignore, etc.) within the network, control, conditions, and series subdirectories (#166).

2. We fixed and improved how HydPy-Meteo-Glob-FAO56 and HydPy-Meteo-Sun-FAO56 calculate extraterrestrial radiation (#192).

   1. Because of following the units of the documented FAO56 equation too closely, both models under- or overestimated extraterrestrial radiation severely for subdaily simulation steps shorter or longer than one hour.
   2. Because of taking the fixed integration bounds of the documented FAO56 equation instead of adjusting them to the time of sunrise or sunset when necessary, both models underestimated extraterrestrial radiation slightly for all possible subdaily simulation timesteps.

   These changes are irrelevant for models that operate on a daily or longer timestep, cause small improvements for models that operate on an hourly timestep, and lead to substantially different evapotranspiration estimates for models that operate on subdaily, non-hourly timesteps. If your model might be affected, we recommend testing the impact of switching to HydPy 6.4 before going operational. We will update HydPy 6.3 for a while to keep it compatible with future changes to the Python ecosystem.