replace WEBP with EXTRAS after moving this file to the top-level folder of the same name Change-Id: Ide4dab027bd09f5df701f1adf2bf896c130a5441
reserve src/ for the code of the main libraries: libwebp, libwebpdemux and libwebpmux + demote this library to internal only; i.e., don't install the header + lib with make install Change-Id: I8c9844db8f494be0fa0a2549a5b75b5cebcf666d