instead of top-level files
- ensure directory is private
- both tljh and jupyterhub config go in there
- move old config.yaml to new location at install time
We do not want users to hand-edit YAML files. This has been a
major source of bugs and confusion for users in z2jh. Doing so
in a terminal text editor makes it even worse.
This lets users type commands directly to modify config.yaml file
rather than edit files directly. This makes it a lot less error
prone and user friendly.
Advanced users can still edit config.yaml manually.
Fixes#38
