add argparser recipe to use commnad line arguments and select opeartions

[mshaikh786]

Hi David,
Here is a suggestion to included argument parsing so that selective operations can be passed via command line to allow restart of the process where it left off (ball park).
Regards
Mohsin

[davidrpugh]

@mshaikh786 I had a glance through the PR. I think it makes sense to create a mechanism that allows the user to specify which of the train, val, or test sets that they wish to prepare. Preparing the training data is particularly time consuming and if has already been done, then there is no reason to do it again. I also like the idea to implement this mechanism as optional boolean flags.

However, I think that the default behavior (i.e., what happens when user runs a script with no args) should be to build everything; but we should allow users to disable the build for training, validation, or testing of data sets if they wish.

Something like to following UI for typical use case...

$ python build-imagenet-datasets.py

...and then something like the following for use who wants to build only validation dataset.

$ python build-imagenet-datasets.py --no-train --no-test

[davidrpugh]

@mshaikh786 take a look at PR #2 which implements the ideas from this PR along the lines of my comment above.