[Issue 401] add more std.gc APIs, e.g. std.gc.allocatedMemory();

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=401

--- Comment #3 from Andrei Alexandrescu <andrei at erdani.com> ---
This looks more like a task than an enhancecement request. @Sean okay to remove
it for now?

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