Remove :item() method and TODO list from AttributeList.lua
Remove :item() method and TODO list from AttributeList.lua

Attributes should be accessed via their parent element. There's no
reason to implement all the pointless NamedNodeMap methods from the DOM
spec.

This isn't a breaking change, since the :item() method was never
actually made available via any metatable.

craigbarnes/lua-gumbo,craigbarnes/lua-gumbo,craigbarnes/lua-gumbo