AMUSE 13

The main change in this version compared to version 12 is that AMUSE is now using Python 3 natively, and cannot be used with Python 2 any more*. Since Python 2.7 will no longer be supported or updated from the end of this year, we highly recommend everyone to switch to Python 3 if you have not yet done so. Converting your own scripts is usually a trivial task using the 2to3 tool**.

*: For those of you who absolutely need Python 2, AMUSE 12 is still available and will receive essential updates for a while.
**: See https://docs.python.org/3.8/library/2to3.html