Allow node data bag path to be configured

Make it possible to configure the `nodes_path` that is used when nodes
are searched. This is similar to `data_bag_path` and `role_path`.
The default is still <data_bag_path>/node/.
Add version to treetop gem to make installation work omnibus setting
Allow newer versions of treetop.
Merge pull request #31 from arjun810/master

Add version to treetop installation so that things work in an omnibus setting
Merge pull request #28 from tmatilai/node_path

Allow node data bag path to be configured
Update installation instructions

Refs #8
more thoroughly document usage with chef 11
Merge pull request #39 from michaelglass/installation_instructions

Installation instructions