The first evolution

Features:

• explicitly set experiment log level based on whether running in debug
  mode.
• Do not catch and except errors in cells when running in debug mode. This should allow a user's debug session to cause a breakpoint on exception
• Add load_trial_data() to load from a particular hextr
• Add py.typed marker

Fixes:

• Allow calls string eval args, e.g. filename
• Allow empty eval args
• Prevent double-runs of experiments caused by importing main and then
  running it.

Backwards incompatible changes:

• mitosis.run returns hexstr, not experiment metrics