openpgp: ECDSA key and signature support

Add support for creating and signing with ECDSA OpenPGP keys

Change-Id: I6d530325ab801ba800187b88e8cfea079cfa41ed
Reviewed-on: https://go-review.googlesource.com/20608
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jacob H. Haven <jacob@jhaven.me>
Reviewed-by: Adam Langley <agl@golang.org>
6 files changed