transforms quarterly data into annual ones
tsout=q2a(tsin,ind)
* tsin = a qurterly timeseries
* ind =
. -1 if the annual data is to be the sum of the corresponding quarters
. 0 if the annual data is to be the mean of the corresponding quarters
. 1 if the annual data is to be the value of the first quarter
. 2 if the annual data is to be the value of the second quarter
. 3 if the annual data is to be the value of the third quarter
. 4 if the annual data is to be the value of the fourth quarter
ind is optional; if not provided, it is set to -1
* tsout = the corresponding annual time series