support configuration with mingw cross-compiled on Linux

prefer lower-case header and dll names
bump Win32 API level to Windows 2003 0x502
fix Win32 compile errors in disk_stats
rename stat_type enumerations in example program to not conflict with builtin Windows types

Windows defines typedefs for INT, FLOAT, etc. that conflight with the
stat_type enumeration. Add STAT_TYPE to these so they can build on
Windows (tested in mingw on Ubuntu 13.10)
update win32 error handling
update user_stats error handling on win32
implement sg_get_sys_page_size on win32
fix various win32 build errors in os_info
fix various win32 build errors with network_stats
fix various win32 build errors with memory_stats
fix build errors if pthreads are not present
resurrect CPU counters for Win32

Performance Data Helpers may be nonsense, but are better than nothing
disable dllexport, this breaks static library builds
disable build of missing manpages