Added UnitTest45 project,

which will be used for .NET 4.5-specific unit tests (e.g. async support).
When Hyprlinkr itself is upgraded to .NET 4.5, this project should be
merged with the standard unit test project.
Added AutoFixture.Xunit NuGet pkg to UnitTest45.
Updated Json.NET to newest version,

because there were inconsistent versions in use across various projects.
Added Newtonsoft.Json NuGet package to UnitTest45

project.
Added Microsoft.AspNet.WebAPI.Core NuGet package

to UnitTest45 project.
Added AutoFixture.AutoMoq NuGet package

to UnitTest45 project.
Added XUnit.Extensions NuGet package

to UnitTest45 project.
Added GetUriAsync method,

in order to support async controllers.
Added a Guard Clause to GetUriAsync.
Added a test for MethodCallExpression.
Added XML comments on GetUriAsync,

as well as suppressed a CA warning.
Aligned assembly version for UnitTest45 project

with all other projects.
Filled out a couple of assembly attributes.
Incremented minor version,

in order to indicate that support for async Controllers is a new feature.
Added licence URL to .nuspec file.
Added UrlHelperExtensions.
Added UrlHelperExtensions unit tests.
Changed name of helper method to GetLink, changed names of unit tests to match.
Added Xunit.Runners NuGet package,

in order to be able to run unit tests from the command line.
Moved NuGet specification to own folder.