Add support for specifying keys

[jacobheun]

libp2p-crypto already supports multiple key formats, this PR exposes that by adding the type option to .create. This will allow users to create the other key types more easily.

[jacobheun]

I am going to do some integration tests against libp2p and js-ipfs with the ed25519 key type and will report back once done.

[jacobheun]

I ran this through the js-libp2p and js-ipfs test suites. I also had the tests alternate the key type (rsa and ed25519) used so that nodes connecting to one another would have different key types.

Aside from a minor issue with the libp2p-websocket-star-rendezvous code not respecting the crypto verify api, everything passed successfully. The issue with the rendezvous code has been fixed.

This should be good to merge.

[vasco-santos]

LGTM! 👍

[jacobheun]

@pgte I rebased this off the latest release, let me know if there are any updates you need from me for this to be released.

[blakebyrnes]

@jacobheun there's a ticket in https://github.com/libp2p/js-libp2p-crypto-secp256k1 to support secp keys in the latest libp2p. You can't unmarshal private keys since the underlying signature changed in peerId (https://github.com/libp2p/js-libp2p-crypto-secp256k1/pulls). Is there any reason to keep secp256 in it's own package at this point? Isn't it directly included in libp2p crypto now? Apologies if this is the wrong place to discuss.

[jacobheun]

@blakebyrnes I created an issue at libp2p-crypto to discuss this libp2p/js-libp2p-crypto#135, since it should probably happen there.

[vasco-santos]

Closing, as this was added on #95