add finegrained timing settings for different folders #1

more of a nice-to-have than a need-to-have... would be nice to set different settings for different targets / roots. for example, prune my targets dirs weekly, but only touch node_modules monthly, etc

not sure how this would even be structured... rough idea is:

rules = [
  {
    roots = [ "$HOME/Projects" ];
    target = "node_modules";
    frequency = "monthly";
  }
  {
    roots = [ "$HOME/university" ];
    target = "node_modules";
    frequency = "weekly";
  }
  {
    roots = [ "$HOME" ];
    target = ".cache";
    frequency = "weekly";
  }
];

not sure how this would play with the existing config...