feat: is multiaddr private and loopback

[vasco-santos]

This PR adds multiaddr isPrivate and isLoopback utilities that can be used for libp2p core and libp2p users to validate if a multiaddr address is a private/loopback network address. This will be useful for creating multiaddr sorters and filtering for dialling and advertising purposes.

Unfortunately, the already installed ip-address module does not support this for ipv4 and ipv6. As a consequence, the private-ip module was added. It has 706 Bytes minified and 312 Bytes minified and gzipped per bundlephobia, which is fine. A is-loopback-addr module was also created for a more specific check.

[vasco-santos]

@jacobheun I created a module is-loopback-addr with a more specific check for verifying loopback addresses and added it. Also structured the utils as you suggested

[jacobheun]

This looks good, just two things:

1. Add the utilities to the README so they're easy to find.
2. Can we add some tests for multiaddrs without IPs? (dns4, etc) Do these functions throw if there is no IP?

[vasco-santos]

I added docs and more tests to both. I noticed other utils had no docs (nor jsdocs) and I will add them in a follow up PR.

Do these functions throw if there is no IP?

Yes, they throw if they are not a network address with /{ip4, ip6, dns4, dns6}/{address}/{tcp, udp}/{port} format. If other type of multiaddrs get here, they should not and I think we should throw

[jacobheun]

LGTM, the headers in the readme are off though.

[jacobheun]

All the following headers are off (too many #'s)

[vasco-santos]

yes, thanks for noticing! fixed it