Add an experimental perf->heaptrack data converter.
Add an experimental perf->heaptrack data converter.

The resulting data file is much smaller than a perf.data file, and
can be visualized with heaptrack_gui. Of course, the labels will be
all off, but this is a good first step towards visualizing perf data
files with the heaptrack code infrastructure.

muojp/heaptrack,muojp/heaptrack,muojp/heaptrack,muojp/heaptrack,muojp/heaptrack