In this commit, a new net.Addr implementation called OpaqueAddrs is
added along with a WriteOpaqueAddrs func that is called in
WriteNetAddrs. It will be used to store any address bytes that we cannot
parse due to us not being aware of the address type.
This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules