Update syntax to be compatible with Rails 4
Convert ancestor and descendant_nodes to scope

Something made me think these wouldn't work as scopes, but @laserlemon
pointed out on the pull request that they would.
Merge pull request #13 from jheiss/rails4

Update syntax to be compatible with Rails 4
Updates to work with Rails 4.x, hat tip to jheiss and laserlemon
first attempt to implement reload parameter on descendants().