BIP 44: add depth layer for compression (or lack thereof) signal

Although most wallets use compressed keys nowadays, for the sake of compatibility and being able to be imported on any potential legacy systems (or any other software/hardware that uses uncompresssed keys), I think it would be good to have an option to signal that a given key should be uncompressed, via an optional additional BIP32 depth layer.

Edit:  I'm new to GitHub, and I'm not sure if I've commented in the right place  -- it's telling me I've requested some commits be merged, which I did not intend.  All I wanted to do was comment my idea for this BIP44 addition.  I apologize if I have not submitted the comment properly or in the correct place.