BackPort to .NET 4.0

[ststeiger]

I've added support for .NET 4.0.

Just 3 small changes necessary, and these additional files:

https://github.com/ststeiger/ChromeDevTools/tree/master/source/MasterDev.ChromeDevTools.DotNet4/Net4

Check if you want to integrate it.

• Replace Task.Run with Task2.Run (2x) to redirect to the appropriate Task-class
• Replace t.GenericTypeArguments with t.GetGenericTypeArguments (1x)
• add Microsoft.Bcl.Async and Microsoft.Net.Http nugets if the target is net4

Install-Package Microsoft.Bcl.Async
Install-Package Microsoft.Net.Http

and finished