Added async "constuctor" for AutoRenewLease

Required adding async targeting pack for .NET 4.0
Added a bunch of other blob/table service async helper extension methods
Updated to latest version of nuget and cleaned up build.cmd
Moved dll project to its own folder + added simple test assembly
Fixed Try acquire/renew lease methods + added Container.CreateIfNotExistsAsync
Removed sync AutoRenewLease constructor

commented out DoOnce/DoEvery until I can updated them to be async
updated tests to break lease with timespan zero
Changed AutoRenewLease to use Rx Interval Observable instead of dedicated thread