(chocolateyGH-8) Convert to SecureString

Add extension for converting a string to a SecureString. This should
return an empty securestring if the value passed in is null or empty.

src/chocolatey/StringExtensions.cs

@@ -17,6 +17,7 @@ namespace chocolatey
 {
     using System;
     using System.Globalization;
+    using System.Security;
     using System.Text.RegularExpressions;
     using infrastructure.app;
     using infrastructure.logging;
@@ -83,6 +84,26 @@ public static string to_string(this string input)
             return input;
         }
 
+        /// <summary>
+        /// Takes a string and returns a secure string
+        /// </summary>
+        /// <param name="input">The input.</param>
+        /// <returns></returns>
+        public static SecureString to_secure_string(this string input)
+        {
+            var secureString = new SecureString();
+
+            if (string.IsNullOrWhiteSpace(input)) return secureString;
+
+            foreach (char character in input)
+            {
+                secureString.AppendChar(character);
+            }
+
+            return secureString;
+        }
+
+
         private static readonly Regex _spacePattern = new Regex(@"\s", RegexOptions.Compiled);
 
         /// <summary>