Update libvpx and incorporate new build system

Move libvpx down a directory. Separate libwebm and rename it. It would
be more accurate to rename external/libvpx to external/webm.

Use file lists directly from upstream libvpx. This allows adding new
targets and new features (such as the encoder) easily. MIPS and x86
options are in progress. See new file "UPDATING"

The new libvpx checkout is not from a release branch. The decoder is
stable but it should be checked and potentially updated if the encoder
is enabled.

Requires I42b51e2845a696a6e211dde00951afc8f571336f which updates
libstagefright to account for new paths and library names.

Change-Id: I739f99d48b8d7e6354c416ef2ca79c954826307f
diff --git a/NOTICE b/NOTICE
index 7a6f995..1ce4434 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,4 +1,4 @@
-Copyright (c) 2010, Google Inc. All rights reserved.
+Copyright (c) 2010, The WebM Project authors. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
@@ -12,9 +12,10 @@
     the documentation and/or other materials provided with the
     distribution.
 
-  * Neither the name of Google nor the names of its contributors may
-    be used to endorse or promote products derived from this software
-    without specific prior written permission.
+  * Neither the name of Google, nor the WebM Project, nor the names
+    of its contributors may be used to endorse or promote products
+    derived from this software without specific prior written
+    permission.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT