Feature/netcore preparation (#2035)

* Move to use package reference for restoring nuget packages.

* Return a task result for this async method.

* Update to a supported version of the .NET Framework. This also has the side effect of allowing us to automatically generate our binding redirects on build.

* Set the solution to target VS2017

* Update test solution csproj file to support being built through MSBuild 15

* Move to use package reference for restoring nuget packages.

* Return a task result for this async method.

* Update to a supported version of the .NET Framework. This also has the side effect of allowing us to automatically generate our binding redirects on build.

* Set the solution to target VS2017

* Update test solution csproj file to support being built through MSBuild 15

* DateTimeRoutines does not have Nuget packages that support .NET Standard (and therefore .NET Core). We will have to include them for now until we can get rid of this dependency.

* Move the interfaces into their own files. This will be useful when we share them between the .NET Core and .NET Framework WebAPI

* Stage services that need to point to the new interface namespace.

* Update CurlSharp to fix memory leak issue and support better runtime compatibility with OSX and Linux

* Start spliting some interfaces into their own files - this will help by allowing us to split them out in the future into a seperate project so the actual implementations can stay within their respective architectures when required

src/CurlSharp/Enums/CurlHttpVersion.cs

@@ -23,9 +23,24 @@ namespace CurlSharp
         /// </summary>
         Http1_1 = 2,
 
+        /// <summary>
+        ///     Enforce HTTP 2 requests.
+        /// </summary>
+        Http2_0 = 3,
+
+        /// <summary>
+        ///     Enforce version 2 for HTTPS, version 1.1 for HTTP.
+        /// </summary>
+        Http2_Tls = 4,
+
+        /// <summary>
+        ///     Enforce HTTP 2 without HTTP/1.1 upgrade.
+        /// </summary>
+        Http2_PriorKnowledge = 5,
+
         /// <summary>
         ///     Last entry in enumeration; do not use in application code.
         /// </summary>
-        Last = 3
-    };
+        Last = 6
+    }
 }