BrowseT offers a uniform interface to traverse constructions from
TypedTree.
Mutually recursive types from TypedTree are wrapped into different
constructors of the type node.
Then type t allows to build a tree of nodes.
Finally the function of_node turns a node into a t tree, which
structure mimics the recursive structure of the TypedTree node.
t also tries to capture the location and environment of node and defaults
to default_loc and default_env otherwise.
Accessors for information specific to a node