Measuring callback invocation time

[varsill]

The idea is to add a simple mechanism to measure how long does callback's invocation takes (for each callback in elements, bins and pipelines) and warn in case it takes longer than assumed threshold value.
It could help in debugging problems where Membrane component becomes unresponsive because it's busy with running a callback.
By default, the threshold could be set to :infinity (for this value we could prune time measurements during compilation so that to make sure we don't affect performance).
This mechanism wouldn't solve the problem where component is infinitely stuck on particular callback invocation, as the warning would be printed when the callback finishes. At the same time, these types of types of problems can be easily debugged with Process.info(:current_function).