Added missing cmath header and added the Unix way of creating a directory

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• The cmath header was missing in ppc_reader.cpp, leaving functions such as floor and pow undefined

• This refused to build on OSs other than Windows due to the Windows.h dependency.

  • I noticed you only used CreateDirectory from Windows.h, so it was an easy fix
  • I wrapped the #include around an #if defined(_WIN32) || defined(WIN32), and put the appropriate Unix header in the else clause
  • I uncommented CreateDirectory and wrapped it around another #if defined ...
  • And I also replaced the \\ path separators with / to prevent unsightly filenames with backslashes (Windows should still accept / as a path separator)

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Fixed already in master - closing