memory_maps on Windows may be wrong

[giampaolo]

Right now it returns rss memory only but according to:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa366775(v=vs.85).aspx
...there's a type distinction we are not taking into account.
Each memory region being processed can either be of MEM_IMAGE, MEM_MAPPED or MEM_PRIVATE type. So perhaps the returned tuple should not have any rss field but instead it should have image, mapped and private (which is the most import in order to calculate USS, see also #746).

[giampaolo]

Apparently all processes I checked are type == MEM_IMAGE so maybe this is correct as it is now.