Added a new option GenerateInternalImports that outputs "__Internal" as the library name for DllImports. Fixes #54.

For more details about what it does:  http://www.mono-project.com/Embedding_Mono#Exposing_C_code_to_the_CIL_universe).

src/Generator/Driver.cs

@@ -261,6 +261,7 @@ namespace CppSharp
         public bool GenerateFunctionTemplates;
         public bool GeneratePartialClasses;
         public bool GenerateVirtualTables;
+        public bool GenerateInternalImports;
         public string IncludePrefix;
         public bool WriteOnlyWhenChanged;
         public Func<TranslationUnit, string> GenerateName;

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -1998,6 +1998,9 @@ namespace CppSharp.Generators.CSharp
                 libName = libName.Substring(3);
             }
 
+            if (Options.GenerateInternalImports)
+                libName = "__Internal";
+
             Write("[DllImport(\"{0}\", ", libName);
 
             var callConv = Helpers.ToCSharpCallConv(function.CallingConvention);