Allow objects of libember::glow::GlowRootElementCollection to be automatic

[GoogleCodeExporter]

At the moment the library forces to use 
libember::glow::GlowRootElementCollection::create() in to create an object of 
this type (and as consequence, a delete is required). Most often, this is not 
required because this object is only used to create a message, serialize it and 
throw it away.

I propose to stop forcing this.

Original issue reported on code.google.com by nullable...@gmail.com on 20 Jun 2013 at 8:34