Implemented lexer

Compiler/Compiler.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Compiler
+{
+    public class Compiler
+    {
+        public static void Main()
+        {
+            TestCompiler("../../../../tests/week_1/valid");
+            TestCompiler("../../../../tests/week_1/invalid");
+        }
+
+        static void TestCompiler(String path)
+        {
+            String[] files = Directory.GetFiles(path);
+            Lexer lexer = new Lexer();
+
+            foreach (String filename in files)
+            {
+                StreamReader file = new StreamReader(filename);
+                String contents = file.ReadToEnd();
+                
+                List<Token> tokens = lexer.Lex(contents);
+                
+                Console.WriteLine("-----------" + filename + "-----------");
+                foreach (Token token in tokens)
+                {
+                    Console.WriteLine(token.ToString());
+                }
+                Console.WriteLine("--------------------------------------");
+            }
+        }
+    }
+}