Depth limit

[bradleyjkemp]

Expected Behavior

Be able to limit the depth to which memviz maps a structure

Actual Behavior

memviz follows pointers arbitrarily far, even if the information I want is actually near the top of the graph.

Example input

Support a MaxDepth option like so: memviz.Config.MaxDepth = 10

[bradleyjkemp]

Dependent on #25