Fixe integration tests when run as a complete fixture.

Previously the test database was created / destroyed on fixture setup /
teardown. This meant that tests were not isolated from each other and some
of the tests would fail depending on the order they were run in. This
commit creates and destroys the database for each test, isolating them.
Update to .NET 4
Update to .NET 4.5
Convert core LoveSeat methods to async / await semantics.

Rename methods to follow MS guidelines, e.g. GetDocument()
becomes GetDocumentAsync().

Return async in all methods where we trigger an http request.
Use JSON.NET from NuGet
Rename LoveSeat projects to LoveSeat.Async.
Update readme
Adjust namespace to LoveSeat.Async
Add ability to pass enumerator into bulk document collection.
Add support for constructing Documents from anonymous objects.