function goLastMonth(month, year){
if(month == 1){
--year;
month = 13;
}
document.location.href = '?month='+(month-1)+'&year='+year;
}

function goNextMonth(month, year){
if(month == 12){
++year;
month = 0;
}
document.location.href = '?month='+(month+1)+'&year='+year;
}