getDocComment() now returns the last comment (given that it is a doc
comment). setDocComment() no longer exists, as it doesn't make sense
with the comment objects anymore. getAttribute() now returns by reference,
so it also works in reference contexts.
Now two arrays are fetched from the lexer: $startAttributes and
$endAttributes. When constructing the attributes for a node, the
$startAttributes from the first token of the node and the $endAttributes
of the last token of the node are merged.
Now the end line is saved in the endLine attribute.
a) ->traverseNode() now operates on a clone of the node, otherwise the original node will be modified too
b) before nodes were passed to the following visitor unchanged, even though they were already changed in the tree
