Right now, if you want to import just one function in bip39 you must import the entire bundle. This can add unnecessary code to already large apps, making them larger. I propose that each function be written in their own files so that they can be imported independently of one another.

My specific concerns here are the the unorm dependency and words list files, which are quite large and not required for all of these utility functions.

Note: I plan to PR this repo with this change, but am open to thoughts in the meantime :)