Base32 address format for native v0-16 witness outputs.

Defines Bech32, the address format starting 'bc1' used for SegWit payments, designed to catch typing mistakes.

Older addresses mix upper and lower case, are awkward to read aloud and take up more room in QR codes. Bech32 uses a single case and a stronger error check, so a wallet can spot almost any mistyped address before money is sent. It was made for the new kinds of output that SegWit added.