The Eclipse bundle unzips to a subdirectory

Modify build.gradle to create a deeper directory structure in the ZIP bundle.

Add a short README.

This is the new structure:

loopback-android-{version}/
 +- README
 +- libs/
     +- loopback-android-{version}.jar
     +- loopback-android-{version}.jar.properties
     +- strong-remoting-android-{version}.jar
     +- strong-remoting-android-{version}.jar.properties
     +- android-async-http-1.4.3.jar
     +- evo-inflector-1.0.1.jar
 +- docs/
     +- loopback-android-{version}-javadoc.jar
     +- strong-remoting-android-{version}-javadoc.jar
 +- src/
     +- loopback-android-{version}-javadoc.jar
     +- strong-remoting-android-{version}-sources.jar