Docstrings waiters

[kyleknap]

This is the final pull request in the series of pull requests that I have been making to add dynamically generated docstrings to clients and resources. I would recommend looking at this pull request last because it includes two previous pull requests, and thus makes it quite large.

In addition, I did a fair amount of refactoring of the resource factory code. With the waiter docstrings, I needed access to a waiter model and that really just added on to the really large signatures used throughout the factories. So I decided to shorten the signatures and make the arguments much more explicit to improve readability by reducing ambiguity. I shortened the signatures by introducing the concept of a ServiceContext where it is just a namedtuple of important information related to the service and adding many of the arguments to this new class. I did this because there was this pattern of where there were some objects that were needed for few spots in the code (and only for reading purposes), but due to the nature of how resources dangle off all other resources it needed to be passed to a dangling class so that it can be passed to other classes that may be generated from it. Thus this allows us to update the code such that if the factory needs any more information, we can add it to this context, instead of having to update the signatures and all of the spots the method is called.

cc @jamesls @mtdowling @rayluo @JordonPhillips

[kyleknap]

Test pass, but the rebasing job was messy here. I would prefer to wait until the collections docstrings are merged. So I can clean this up a bit more.

[kyleknap]

Alright the commit history is much better now. No longer blocked for this one.

[jamesls]