v15 Config

[alex-rakowski]

Add global configuration settings

Allow py4DSTEM functions to search for globally defined settings rather than requiring args/kwargs set per function call.

py4DSTEM.config.set_GPU(True) or py4DSTEM.config = {'GPU' : True}, etc.

• Determine minimal implementation that will not break the existing code.
• Workout which settings should be stored in global config.
• Determine how ephemeral the config is - per session vs stored in a file and loaded.
• Determine how global config is overruled by local args/kwargs.
• create new functions that search for global config and args/kwargs.