* *: Import `libp2p` with `default-features = false`
While not a win in most cases, it reduces compile time for tests of
individual crates.
* Cargo.toml: Set features for examples
A `ProtocolsHandler`, now `ConnectionHandler`, handels a connection, not
a protocol. Thus the name `CONNECTIONHandler` is more appropriate.
Next to the rename of `ProtocolsHandler` this commit renames the `mod
protocols_handler` to `mod handler`. Finally all combinators (e.g.
`ProtocolsHandlerSelect`) are renamed appropriately.
