We are currently using the `base58::Error` type to create errors in
`bitcoin`, these are bitcoin errors not `base58` errors.
Note that we add what looks like duplicate
`InvalidBase58PayloadLengthError` types but they are different because
of the expected length. This could have been a field but I elected not
to do so for two reasons:
1. We will need to do so anyways if we crate smash more
2. The `crypto::key` one can have one of two values 33 or 34.
With this applied we can remove the now unused error variants from
`base58::Error`.
In preparation for improving the `base58` error types crate an `error`
module and move the single current error type there. Make the module
public and reexport the type.
Add a new `base58` crate to the workspace and move the `bitcoin::base58`
module to it.
Done as part of crate smashing, specifically so that we can make `bip32`
into a separate crate.
Tobin C. Harding
Liam Aharon