cygwin pathsep fix

  #include <windows.h>
defines _WIN32.
So the subsequent
  #if defined __mingw32__ || defined _WIN32 || defined _MSC_VER
fails for cygwin, leading  at every cpan start to

cygwin warning:
  MS-DOS style path detected: /tmp\.UUID_STATE
  Preferred POSIX equivalent is: /tmp/.UUID_STATE
  CYGWIN environment variable option "nodosfilewarning" turns off this warning.
  Consult the user's guide for more details about POSIX paths:
    http://cygwin.com/cygwin-ug-net/using.html#using-pathnames
suggest Data::GUID as an alternative
add a bit of docs on namespaces
github links
replace use vars with our
changelog, version