Add key conversion tools

[michaelhall923]

For securely converting between hex and bech32, as well as betweeb nsec/npub and hex priv to hex pub.

Ex. noscl convert --npub d23b81da2b83cdb821cd3b8dbcac393943ba9cd

Output npub1b6asdtbf68astd6f7863fnt76a4f7as78as