Resolve "(LearnerND) add iso-surface plot feature"

Closes #112 (closed)

docs/source/docs.rst

@@ -25,7 +25,7 @@ Meta-learners (to be used with other learners):
 
 - `~adaptive.BalancingLearner`, for when you want to run several learners at once,
   selecting the “best” one each time you get more points,
-- `~adaptive.DataSaver`, for when you function doesn't just return a scalar.
+- `~adaptive.DataSaver`, for when your function doesn't just return a scalar or a vector.
 
 In addition to the learners, ``adaptive`` also provides primitives for
 running the sampling across several cores and even several machines,