reconsider the names of Node::paths() and NodeIterator::path() methods

[cyrush]

We are adding a path() function that returns a string with the full path to the given node

has_path and fetch path variants descend the tree, but, the new path() clashes a bit with a few other uses "path" in method names:

For example, in the Node and Schema classes:

• the two paths() variants list the names of the node's direct children, not full paths to them.

In the NodeIterator class:

• path() returns the name of the child, not the full path to the current child

I propose changing the path variants in the Node and Schema classes to

• child_names() (or similar: names_of_children() , is closer in style to number_of_children())

And path() in NodeIterator to:

• name()

It's an API breaking change, but I think 0.2.0 is the right time to do this.

[cyrush]

spoke with Brian Ryujin & @xjrc about this, both concur it make sense to make a change.
going to go with

child_names() for the paths() methods in Node & Schema

and name() for the path() method NodeIterator

[cyrush]

resolved in #71