New extension: scrub

[paralin]

Proposal: new extension called scrub which adds a function Scrub() to messages.

Similar to Reset(), except it recursively overwrites all buffers & fields in the message with zeros.

[vmg]

Can you elaborate on why would you find this useful? I'm not opposed to it in principle, but I can't think of an use case off the top of my head!

[paralin]

If the Protobuf messages contain something sensitive you want to clear just after processing so that the value isn't left in the heap