Replace deprecated Win API calls in Win32_EntropySource

[neusdan]

• GetTickCount is replaced by GetTickCount64(): see https://msdn.microsoft.com/en-us/library/windows/desktop/ms724408(v=vs.85).aspx for details
• GlobalMemoryStatus is replaced by GlobalMemoryStatusEx: see https://msdn.microsoft.com/en-us/library/windows/desktop/aa366589(v=vs.85).aspx for details

[randombit]

Hm, the advantage here is fairly minimal since this is just for entropy gathering, but I do see that the old MemoryStatus call is documented as failing (returning -1 in the fields) if the machine has over 4G of memory, which these days is most of them, so using Ex would be more likely to generate good results. Looks like support for TickCount was added in XP/2003 and MemoryStatusEx in Vista/2008. So this would break support for very old systems (XP/2003) but as both are EOLed by MS anyway I'm inclined to see that side effect as a feature :) and anyway support for XP is AFAIK completely untested and so hypothetical in any case

[neusdan]

I'm fine with dropping support for Windows XP :-)