CCT v0.7.0

Improved consistency across pullAncestors() and getDescendants() with the use of attribute. Can now use custom hierarchies from yaml.

When searching for a node with pullAncestors or getDescendants if the node is missing a NULL will be returned by default, an empty vector for vector=T and an empty dataframe for table = T. Minor guard rails have also been added to replace inscrutable error messages when searching for non-existent nodes.

A new parameter has been added to each of the above functions attribute. This allows the resulting vector/table/node network to use other metadata than "lineage" when reading from data.tree networks. The most likely use of this will be in reading custom hierarchies from yaml where the protected data.tree label "name" can be substituted for "lineage" and retrieve metadata from the network.