Ensure Bech32.encode throws for output length > 90

[webmaster128]

The bech32 spec says an address is no longer than 90 characters. To avoid any kind of decoding trouble later on, we should ensure this library throws when the result address exceeds 90 characters.

For decoding on the other hand there is no reason to enfore this restriction. Here we could even test if the current implementation supports very long addresses.

Some sample data here: cosmos/cosmos-sdk#6237