Added new python string builder class

src/Bonsai.ML.HiddenMarkovModels/PythonStringBuilder.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Text;
+
+namespace Bonsai.ML.HiddenMarkovModels
+{
+    public abstract class PythonStringBuilder
+    {
+
+        private string _cachedString;
+        private bool _updateString;
+        protected readonly StringBuilder StringBuilder = new StringBuilder();
+
+        protected void UpdateString()
+        {
+            _updateString = true;
+        }
+
+        protected virtual string BuildString()
+        {
+            return StringBuilder.ToString();
+        }
+
+        public override string ToString()
+        {
+            if (_updateString)
+            {
+                _cachedString = BuildString();
+                  _updateString = false;
+            }
+            return _cachedString;
+        }
+    }
+}
+
+