Added bunch of javadocs and restricted some visibility.

No functional changes

src/main/java/org/scribe/model/Token.java

@@ -1,11 +1,21 @@
 package org.scribe.model;
 
+/**
+ * Represents an OAuth token (either request or access token) and its secret
+ * 
+ * @author Pablo Fernandez
+ */
 public class Token
 {
-
   private final String token;
   private final String secret;
 
+  /**
+   * Default constructor
+   * 
+   * @param token token value
+   * @param secret token secret
+   */
   public Token(String token, String secret)
   {
     this.token = token;