Add appengine-api-1.0-sdk-1.8.3-javadoc.jar

Downloaded as part of Google App Engine SDK for Java
http://googleappengine.googlecode.com/files/appengine-java-sdk-1.8.3.zip

Javadocs repackaged as jar with:

    jar cf appengine-api-1.0-sdk-1.8.3-javadoc.jar -C appengine-java-sdk-1.8.3/docs/javadoc .