Add new files 'build.xml' and 'jamruby_build_config.rb'.

build.xml:
  This file is a build script for Ant.
  And it's auto-generated script by this command 'android update project -p .'.

jamruby_build_config.rb:
  This file is a build script for mruby.
  And this script includes the code to build binaries for Android.