Async cleanups

[ReedCopsey]

This is work for issue #61 - Cleanups of the Async docs.

Note that many code samples didn't port - I pulled them (verbatim) from cached versions of the old MSDN docs.

[smoothdeveloper]

@dsyme, can we have a viable access to the current / MSDN quality documentation until we are done porting the markup?

It's not really workable to use google cache or webarchive (navigating from msdn root to F# pages...) for each and every snippet of code which was mangled in the initial drop, google cache circle buffer is soon overlapping, webarchive is getting slower with axis of time.

My recommendations (but I have no clue of technical implications, although shouldn't be harder than what we currently have to go through) would be to just let msdn website expose the current documentation while we work on preview.msdn based off this repository.

[smoothdeveloper]

@drvink mentioned that https://msdn.microsoft.com/en-us/library/dd233154%28v=vs.120%29.aspx is still accessible which solves the issue I was talking about in above comment.

Please don't change this!

[dsyme]

@smoothdeveloper Questions to @dend please - I'm just an occasional reader here :)

[dend]

@smoothdeveloper @ReedCopsey - what @dsyme said :) I should be your point of contact for doc issues and infra work. That said, your current workaround is one that we are using ourselves for fixes.

[smoothdeveloper]

@dend, heard I won't bother Don here anymore, he has already enough work with all people interacting in visualfsharp repository 😄

Yes, please make sure the msdn pages are still available through the link, I made a PR to show the link in the main README.md of this repository as well so we don't have to search too far for it.

Thanks!