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Bite 66. Calculate the running average of a sequence

Write a function that takes a sequence of items and returns the
running average, so for example this:

running_mean([1, 2, 3])

returns: [1, 1.5, 2]

You can assume all items are numeric so no type casting is
needed.

Round the mean values to 2 decimals (4.33333 -> 4.33). See the tests for more info.

Bonus: use a function of itertools + make it a generator, but this is not required to get this working.