Our encoding/decoding support for scripts is currently a bit convoluted.
Add an example that shows how all the APIs go together.
Note this highlights a potential problem. `to_hex_string` is in
`bitcoin` and therefore has access to consensus encoding but does not
include the length prefix. This means that the output string from
`to_hex_string` cannot be parsed with
`consensus::encode::deserialize_hex` - which is surprising and has lead
to difficulty by at least one user trying to debug.
Tobin C. Harding