Added Facebook Api and example

src/main/java/org/scribe/builder/api/FacebookApi.java

@@ -0,0 +1,16 @@
+package org.scribe.builder.api;
+
+import org.scribe.exceptions.*;
+import org.scribe.model.*;
+
+public class FacebookApi extends DefaultApi20
+{
+  private static final String AUTHORIZE_URL = "https://graph.facebook.com/oauth/authorize?response_type=token&client_id=%s&redirect_uri=%s";
+  @Override
+  public String getAuthorizationUrl(OAuthConfig config)
+  {
+    if(OAuthConstants.OUT_OF_BAND.equals(config.getCallback()))
+    	throw new OAuthException("Facebook does not support oob authentication.");
+    return String.format(AUTHORIZE_URL, config.getApiKey(), config.getCallback());
+  }
+}