Convert a full month name to a numeric value
switch_full(month)
a character string which will correspond to the numeric value of the input month, i.e. ("01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12")
a character string specifying one of the twelve months, i.e. ("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December")