Proper fix for the time variable

* Use month-centered times in default input file.
* Use interval-centered times in output file.
* In turn, the number of interpolation points --interpolate-n now equals the number of intervals, and time dimension length in output file.
* Change default --interpolate-n from 53 to 52.
* Rework interpolation method to extend annual cycle both ways.
Add standard deviation in fake climate file