make AbstractTrees.print_tree(node) work

[anandijain]

I feel like this shouldn't be too hard and I'd like to make a PR to be able to print_tree(node), opening issue in the meantime

this would be incredibly useful

[anandijain]

AbstractTrees.children(n::EzXML.Node) = elements(n)
AbstractTrees.printnode(io::IO, node::EzXML.Node) = print(io, getproperty(node, :name))
AbstractTrees.nodetype(::EzXML.Node) = EzXML.Node
print_tree(xml)

thats basically it