[Twisted-Python] Combining eventually and incremental dependencies

[Adi Roiban]

This is based on my review of https://twistedmatrix.com/trac/ticket/9111

Is there any real value in having many small python packages doing
only a few things?

Can we pack the deprecation code together with the versioning code...
for example to only have 'incremental' ?

I feel like we are going to the node.js path where you have a package
for the strip function.

I feel that having multiple separate project just adds a lot of extra
admin works... set up repo permissions/ set up pypi access / set up CI
integration / set up documentation.

In the same time, I feel that deprecation and versioning
functionalities are related.

From what I can see in the current examples, each time you use
eventually you are forced to use incremental so that you can pass that
bloody Version instance, which I don't know why we can't go with just
a tupple :)

Thanks!