transport and discovery modules: use a function instead of a class

[pgte]

Currently, you can define a transport or discovery module as an instance or a class.
Instead of a class, why not a function call here and here? This way, the provider has control over which instance to deliver to libp2p.

Use case: this allows me to solve peer-base/peer-base#1

[jacobheun]

What data would you want to see passed into that function? I assume you are talking about using generators for the transports and discovery modules?

[pgte]

Ideally I would like the peerInfo or peerId to be passed in.
This is more about the interface being a function and not a class.
The arguments of this call is being explored in #222.

[achingbrain]

This has been refactored. Closing due to staleness.