Implementation of validation/resize classes

[Maw-Fox]

Features

• When --resize is True, --data_migration (default: True), data migration would create a clone of the relative path to the dataset path, and output %DATASET%_cropped adjacent to the dataset directory. This is to make sure this expensive operation is only run once.
• Currently the .load() operation substantially extends validation time (from ~1000f/s to ~100f/s), while being more extensive it feels like for already-prepared datasets the slowdown is not worth it, despite the lack of verbose debugging upon hitting truncated/corrupted files. Subsequently the addition of --extended_validation (default: False) would allow users to easily perform one-time extended validation.
• The conversion to 3-channel RGB would be moved into the --resize default migration, further speeding up operations on already-validated datasets.
• Addition of skip_validation argument for already-validated datasets to speed up the loading procedure.

[Maw-Fox]

parser.add_argument('--foo', action='store_true')
parser.add_argument('--bar', action='store_false')
parser.add_argument('--baz', action='store_false')
parser.parse_args('--foo --bar'.split())
>> Namespace(foo=True, bar=False, baz=True)

docs

[harubaru]

Resolved some merge conflicts due to PR #40, as a side-note the args being type bool was intentional for an unrelated workflow. Going to test to see if the changes work in a bit.

[Maw-Fox]

Resolved some merge conflicts due to PR https://github.com/harubaru/waifu-diffusion/pull/40, as a side-note the args being type bool was intentional for an unrelated workflow. Going to test to see if the changes work in a bit.

No rush, let me know if any changes need to be done. I had done some rudimentary testing up until the argparse commit, hopefully everything passes. Perhaps it's time to look at some automated testing for PRs and local repos.