Pass the context node (rather than the root node) node within the
NodeMap constructor, so we don't need to keep providing the context
directory on each method invocation.
Mark method as private that is only ever used internally.
Updated MemoizedValue so that it no longer relies on a BRJSNode rather
than a plain Node, in preparation for use of MemoizedValue within
NodeMap.
Final changes so that NodeMap can succesfully make use of MemoizedValue
within a real BRJS application -- but not enabled since many of the
legacy tests rely on constructing with non existent directories, so it
will be helpful to wait until these have first been deleted. I recorded
~10% speed of the cold loading time for the DashboardLoadingTest on my
machine.
Merge pull request #578 from BladeRunnerJS/memoize-node-map-class

Memoize node map class