🚀 go-pugleaf

While imitation is the sincerest form of flattery, the graphical
statistical profiler in Composer seems to be missing some of what I thought
were key elements of SPY: 

a) thresholding
	Eliminate from the display those functions responsible for less than
	a given percentage of the time.

	This is important to reduce the complexity of the display.

b) merging
	Flexible control over merging information about the same function
	when it appears in different parts of the graph.

c) rerooting
	the ability to obtain sub-trees with more detail than the main
	graph.

d) visual display of importance
	Making the height of the boxes proportional to the percentage of
	time seemed to work OK as a way of giving a quick visual indication
	of what functions were really important. It is hard to see that
	73 and 78 and  are a lot closer than 37 and 87.

I think only merging is tricky -- I spent a couple of weeks trying to get
the algorithm right. Its tricky mainly because of recursive merging.