Drop support for Python 2.7, and <3.7 ?

[MichaelClerx]

Testing is being dropped (again): actions/setup-python#672

Upgrading 3 is easy, using virtual environments is getting popular on systems where users don't have full control, so might as well go straight for 3.7+ then?

[MichaelClerx]

Stuff that might be nice for Myokit:

• 3.0
  • No more from __future__
  • New style constructors (super(), and no (object) after every class)
  • No more basestring and needing to think about bytes when handling strings (less of it, anyway)
  • keyword-only arguments
  • exception chaining (raise from), and easier access to tracebacks
• 3.4
  • enums
  • pathlib
• 3.5
  • os.scandir
• 3.6
  • f-strings
• 3.7
  • Ordinary dict is now ordered (by definition, not as an implementation detail)

[MichaelClerx]

But the bigger benefit would just be less clunky code and less testing

[MichaelClerx]

At the same time, it's not a lot of work maintaining 2.7 right now. Github might go back on their decision (again), or an easy docker fix or something might show up...