Rename source type parameters to H

[busti]

This PR renames all type parameters that use the Source typeclass to H[_] : Source.
All the others already are consistently named so why Source too...
We now have:

• F[_] : Sync (or Effect and so on)
• G[_] : Sink
• H[_] : Source

This is in preparation for adding F[_] : Sync effect types to onNext, onError and subscribe to avoid ambiguities with the other parameters.

There are some usages of Sink and Source named SI[_] : Sink and SO[_] : Source respectively. Should these also be renamed accordingly? Also GA, GB, SA and SB are sometimes used. Should I rename the latter to HA and HB?

[cornerman]

Nice! That is a good idea.

From my side, you can rename all of them including SI, SO, GA and so on. Definitely makes it more consistent. Feel free to improve the naming as you see fit :)

[busti]

This should be good to go.

[busti]

One should never be too sure.
Caught that one just in time.

Should be good to go for real this time.

[cornerman]

Nice! Thank you :)