BIP173 specifically calls out that encoders must always output an all
lowercase bech32 string and that the lowercase form is used when
determining a character's value for calculating the checksum.
Currently, the implementation does not respect either of those
requirements.
This modifies the Encode function to convert the provided HRP to
lowercase to ensure the requirements are satisfied and adds tests
accordingly.
The bech32 format is used to encode base32 data
in a string format specified in BIP 173. This is
among other things used to encode native segwit
addresses, also specified in the same BIP.
This commit adds the package bech32, which
contains the necessary utility methods to create
bech32 encoded strings from arbitrary data.
