These functions are prefixed DW which stands for Dark Wallet. The code for the
Dark Wallet address format can be found here:
https://github.com/darkwallet/darkwallet/blob/develop/js/util/stealth.js
Note that I deliberately support only the simplest possible format, which is
where there is only one payload pubkey and the prefix is blank. I should now go
back and replace my old toString, fromString, toBuffer, fromBuffer functions
with these Dark Wallet versions, since they are much more well-thought out than
mine.