Functoria.ContextUniversal map of keys
val new_key : string -> 'a keynew_key n is a new key with name k.
val empty : tempty is the empty context.
add k v t is t augmented with the binding (k, v). Any previous binding of k is removed.
find k t is v is the binding (k, v) has been added to t, otherwise it is None.
merge ~default t merges t on top of default. If a key appears in both default and t, the value present in t is kept.
val dump : t Fmt.tdump dumps the state of t.