Regenerate LLVMSharp using unsafe bindings. (#105)

* Moving the wrapper types out of the generated folder.

* Adding the NativeTypeNameAttribute file

* Moving files that extend the generated types to an extensions folder.

* Regenerating the LLVMSharp sources and cleaning up the wrapper types.

* Cleaning up the unit tests

* Deleting the LLVMSharp.API namespace and supporting bits.

Author: tannergooding

Directory.Build.targets

@@ -27,6 +27,7 @@
     <PackageReference Update="Microsoft.NET.Test.Sdk" Version="16.1.1" />
     <PackageReference Update="NUnit" Version="3.12.0" />
     <PackageReference Update="NUnit3TestAdapter" Version="3.13.0" />
+    <PackageReference Update="System.Memory" Version="4.5.3" />
   </ItemGroup>
 
 </Project>