Cached the file-related properties of TranslationUnit to avoid the performance cost.

Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>

src/AST/TranslationUnit.cs

@@ -31,28 +31,39 @@ namespace CppSharp.AST
         /// Contains the path to the file.
         public string FilePath;
 
+        private string fileName;
+        private string fileNameWithoutExtension;
+
         /// Contains the name of the file.
         public string FileName
         {
-            get { return Path.GetFileName(FilePath); }
+            get { return fileName ?? (fileName = Path.GetFileName(FilePath)); }
         }
 
         /// Contains the name of the module.
         public string FileNameWithoutExtension
         {
-            get { return Path.GetFileNameWithoutExtension(FileName); }
+            get
+            {
+                return fileNameWithoutExtension ??
+                    (fileNameWithoutExtension = Path.GetFileNameWithoutExtension(FileName));
+            }
         }
 
         /// Contains the include path.
         public string IncludePath;
 
+        private string fileRelativeDirectory;
+        private string fileRelativePath;
+
         public string FileRelativeDirectory
         {
             get
             {
+                if (fileRelativeDirectory != null) return fileRelativeDirectory;
                 var path = IncludePath.Replace('\\', '/');
                 var index = path.LastIndexOf('/');
-                return path.Substring(0, index);
+                return fileRelativeDirectory = path.Substring(0, index);
             }
         }
 
@@ -60,7 +71,8 @@ namespace CppSharp.AST
         {
             get
             {
-                return Path.Combine(FileRelativeDirectory, FileName);
+                return fileRelativePath ??
+                    (fileRelativePath = Path.Combine(FileRelativeDirectory, FileName));
             }
         }
     }