Starts a local web server to serve the contents of tree.
If no tree is supplied, serve uses the current tree (from the command line, that will be the current folder). To serve the current folder:
$ ori serve
Server running at http://localhost:5000
The server translates requests for a web route like a/b/c into a traversal of the tree, traversing the keys a, b, and c, then returning the value from that point in the tree.