Added bunch of javadocs and restricted some visibility.

No functional changes

src/main/java/org/scribe/exceptions/OAuthParametersMissingException.java

@@ -2,6 +2,11 @@ package org.scribe.exceptions;
 
 import org.scribe.model.*;
 
+/**
+ * Specialized exception that represents a missing OAuth parameter. 
+ * 
+ * @author Pablo Fernandez
+ */
 public class OAuthParametersMissingException extends OAuthException
 {
 
@@ -9,6 +14,11 @@ public class OAuthParametersMissingException extends OAuthException
   private static final String MSG = "Could not find oauth parameters in request: %s. "
       + "OAuth parameters must be specified with the addOAuthParameter() method";
 
+  /**
+   * Default constructor.
+   * 
+   * @param request OAuthRequest that caused the error
+   */
   public OAuthParametersMissingException(OAuthRequest request)
   {
     super(String.format(MSG, request));