* Implemented `sign_prehashed` for `eth::Keypair`
* missing import
* fmt
* Implemented `sign_prehashed` for `ecdsa::Keypair`
* use `[u8; 32]` type
* ditched From impl
* add ethereum example
The ethereum config doesn't work with the default PolkadotConfig which
this shows how to do.
Tested with a frontier node
* address grumbles
* Update subxt/examples/tx_basic_frontier.rs
* Update subxt/examples/tx_basic_frontier.rs