argument-parsing

It might be useful to provide some kind of error classes as part of this package.
For example, I use code like this:

from argparse import ArgumentError, ArgumentParser

def file_path(x: str):
   d = Path(x)
   if d.is_dir:
      raise ArgumentError(f"{d} is a directory")
   return d

parser = ArgumentParser()
parser.add_argument('output_file', type=file_path, help="Path to 

simple-parsing is simply awesome (thanks!). I'd like to suggest a feature that is crucial for parsing nested args, in my opinion, and the support of other researchers in my group. Here is a minimal example to make things clear:

from dataclasses import dataclass
from simple_parsing import ArgumentParser, ConflictResolution

@dataclass
class WandbArgs:
    dir: str = ''  # Wandb run ca