Dropping Support for Python 2.x

[Kyle Mandli]

Hi everyone,

Per the discussion in issue #162 some of us are thinking of dropping support for Python 2.x.  This is partially motivated by the NumPy and SciPy core teams dropping support for Python 2.x starting at the end of this year.  We would follow a similar path to what is described in the NumPy/SciPy note about dropping support where we would tag the last compatible version of Clawpack and install that if requested by a Python 2.x installation.  The proposed version to do this for is 5.7.0 so this transition is still a little ways off so that people can both prepare or raise issues with the plan.  If you want to join the discussion please do so in the issue mentioned linked above.

Kyle