Modify for new mlpd format.

[omanuke]

I modified heap-shot reader to work with new mlpd format which Xamarin.Profiler 0.34 generates. I asked about this format chang at mlpd file format has changed? and RodorigoMoya told me new format is written in comment of proflog.c. So I saw it and modified.

Modified heapshot.reader can read new mlpd format without error,but I'm not sure this modification is enough.

For example, comment said TYPE_SAMPLE_HIT have mbt_count and method,but it seems that there isn't in genereated mlpd file.

And this modified heapshot.reader may not work for old format.