dev/data organization

The idea is that each dataset has a .py file here in the root of dev/data, and each dataset then creates a directory here, and writes and caches anything inside that directory. So for example:

• running python tinystories.py will create a directory tinystories with its .bin files inside it
• running python tinyshakespeare.py will create a directory tinyshakespeare with its .bin files inside it

And so on. This way we can nicely organize multiple datasets here, share common utilities between them, and then point the .py/.c code in the root of the project accordingly to these.