title: Need to get the dates of all mondays in a year
body: <p>I need to sort data on a weekly base and all i have are dates in a logfile. 
  Therefore to sort out data per week i would like to create a list with the dates of all mondays for a given year. I have tried to work something out and the only idea i currently have is to use ncal with year and month as argument looping over all months and extracting all mondays. Isn't there a more efficient way?</p>