Added Parser

- can parse a basic token list to an AST

Compiler/Parser/Exceptions/InvalidIdentifierException.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Compiler.Parser.Exceptions
+{
+    public class InvalidIdentifierException : Exception
+    {
+        private string value { get; set; }
+
+        public override string Message { get; }
+
+        public InvalidIdentifierException(string value)
+        {
+            this.value = value;
+            this.Message = "Unexpected Identifier " + this.value + ".";
+        }
+    }
+}