b3ea8ccb7 Simplify Base32 and Base64 conversions (Pieter Wuille)
3296a3bb7 Generalize ConvertBits (Pieter Wuille)
Pull request description:
Generalize `ConvertBits` a bit to also be usable for the existing Base32 and Base64 convertions (rather than just for Bech32).
Tree-SHA512: 3858247f9b14ca4766c08ea040a09b1d6d70caaccc75c2436a54102d6d526f499ec07f5bdfcbbe16cbde5aae521cd16e9aa693e688a97e6c5e74b8e58ee55a13