Merged both NuGet packages into one
Brought async primitives project up to spec

Applied common code formatting rules, common project settings (warnings
as errors, overflow checking) and fixed up minor surface defects in the
code such as invalid namespacing.
Removed needless attribute
Added message about NuGet package to readme
Added automatic test account population with data

Test accounts are now automatically populated with the right data - all
the developer needs to do is to set up two accounts and tell the test
harness about them (see TestData class documentation for more info).

AsyncCoordinationPrimitives were removed because they were exhibiting
flaky behavior in the updated tests; they were replaced with
SemaphoreLock from the Useful library, which is working well.
Unavailable items are now hidden by the API

If Mega provides us with items that we do not have a key for or items
that have invalid data (e.g. a file without a size), the API just hides
this item and continues as if it did not exist.

This greatly simplifies API usage, since you never really care about
such weird cases, you only want to focus on the positive scenario.
Simplified usage example in readme