Adds method for retrieving ancestors and current node.
Adds getAncestorsAndSelfWithoutRoot()

Method for retrieving all ancestors of a node, including self, but
excluding the root node.
Adds getAncestorsWithoutRoot()

Method for retrieving all ancestors of a node, but
excluding the root node.
Adds test for getNeighbors.

Modified getNeighbors implementation to call array_values on filtered
neighbors output in order to re-index the array to start at zero. Depending on
where a child landed, the filtered neighbors would be missing the corresponding
index.  This change normalizes that.
Adds getNeighborsAndSelf

Method for retrieving current node and its neighbors.
Adds isRoot method to NodeInterface.
Adds isChild method.
Updates documentation to reflect added Node methods.
Removes *WithoutRoot methods.
Merge branch 'mdwheele-additional-accessors'
Updated README.md