`Serialize` and `Deserialize` implementation for ECDSA `VerifyingKey` was (accidentally?) removed

[shadowcpy]

The serde feature does not activate Serialize or Deserialize for VerifyingKey, as the corresponding code has been removed (by accident?) and docs are not updated.

[tarcieri]

I think what changed is it now requires the pem feature.

That's not entirely ideal. We'll try to get that fixed in the next release so you don't need to enable anything more than serde.

[tarcieri]

I fixed the upstream issue here: RustCrypto/traits#1245

Unfortunately it won't be available until the next minor release of the elliptic-curve crate.

In the meantime, try activating the pem feature.