Adds max-word-length as argument to script

[osilkin98]

In the makemore series, the max word length for the basic MLP was 3, which was nice because you could tune hyperparameters much quicker.
The current implementation simply calculates the maximum length of an item and uses that as the maximum block size.

This update simply allows users to provide a --max-word-length argument if they want to be able to still use 3, 8, or some other arbitrary value.

Signed-off-by: Oleg [email protected]