Moves all of the content from `bitcoin/p2p` into `p2p`.
`TryFrom<Network>` must be implemented for `Network -> Magic` now that
`Network` is a foreign, non-exhaustive type. Ser/de test is updated
accordingly, as well as the `Magic::from_network` constructor, which I
have opted to return an `Option<Self>`. The `TryFrom` implementation
uses a new `UnknownNetworkError(Network)` that mirrors the `Magic ->
Network` error.
The example handshake does not generate a random nonce for the version
message, as there is no `rand` dependency in this crate and the program
only makes a single, user-defined connection.
It appears we can do better than copying and pasting the consensus
encoding macros and functions from `bitcoin` without doing weird
cross-crate macros that require some special knowledge of the crate to
know when they will compile.
Peer to peer messages change on occasion, and we would like to add
messages as they are release from Bitcoin Core. Add an empty crate to
take the crate name.
Fmt Bot
rustaceanrob