feat: Add a config

[calvinmcelvain]

Summary

Create editable configs for customization.

Motivation

Config ideas:

• auto-prune: Removes done items automatically. Defaults to False.
• sublist-delimter: The delimiting character to use to create sublists. Defaults to ".".
• default-priority: The default priority to add to new tasks. Defaults to "medium".
• sort-by: The variable to sort tasks by. By default "id".
• default-colors:
  • inbox: The default color to give inbox. By default "white".
  • list: The default color to give new lists. By default "white".
  • sublist: The default color to give new sublists. By default "white".
  • subsublist: The default color to give new subsublists. By default "white".
• default-list: The default list to use when invoking todo .... By default, "inbox".

Possible Implementation

Store in TODO_DIR/.taskli.json (add to reserved names).