Add support for @ prefixed attrib. in paths

[JorgeCepeda]

Citing the thread in jackson-future-ideas#66, I'd like to be able to access attributes using @ in a path:

xml = "<a b=\"attrib\"><b>node</b></a>"

and as path: "/a/@b" for the attribute and "/a/b" for the node This feature is not available in the latest version 2.14.2