Use JSON.NET from NuGet
Add ability to pass enumerator into bulk document collection.
Add support for constructing Documents from anonymous objects.
Replace usages of ExpectGet with SetupGet.

Moq has deprecated ExpectGet.
Update ViewOptions to use Stringbuilder
Use ConfigureAwait(false) for internal async / await calls.

This is really ugly, but considered good practice in an async API where we
don't know who our consumers are (e.g. WPF / ASP.NET). This shouldn't make
any difference to ASP.NET usage but, for UI consumers, this will prevent
deadlocks and unnecesary context mashalling.
Close http responses in CouchBase.cs. Fixes #31
Cope with null response stream in GetResponseString.