split out XS::Element::Container to make it easier to document

--HG--
rename : lib/Devel/XS/AST/Element.pm => lib/Devel/XS/AST/Element/Container.pm
ensure that EOF's only affect lib/Devel/ParseXS/Stream.pm or  as specified
document a few things

--HG--
extra : amend_source : 1a80ce1ae3992c8abe944ff708494ac4831eb240
update build infrastructure
don't import Extutils::Typemaps::tidy_type