Add TimeGenerated to the output of Windows Event Logs

Updated read_win_el.c to include TimeGenerated from an EVENTLOGRECORD
formatted into a human readable format for better logging. Also updated
the decoder to handle this change.

Original Pull Request: https://bitbucket.org/jbcheng/ossec-hids/pull-request/23/add-timegenerated-to-the-output-of-windows/diff