Update to follow latest mruby.
And fix warning.

Fix:
  - remove 'mrb_class_new_instance_m'.
  - add 'mrb_obj_new'.
  - remove 'mrb_obj_call_init'.
New feature to instantiate Java object is added.
And method lookup for overloaded method is implemented.
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.
Remove DeleteLocalRef() after use safe_local_ref because we continue using the reference.
* More information: http://android-developers.blogspot.com.br/2011/11/jni-local-reference-changes-in-ics.html