calib_cws()

[eva0marques]

Create a function calib_cws(x, ref) to remove systematic bias in the cws dataset.
Default ref = output from download_ghcnh() but users will be able to add its own network.
Note: systematic bias varies across the hours of the day, and also across the seasons. So it might be relevant to create a moving average to remove it.

[eva0marques]

1. Select all observations in x at less than x meters from a ref station (param option: distance x in meters)
2. Measure the anomaly in temperature for these observations in regard to the ref
3. Compute the average bias (param option: per hour of the day)
4. Remove this bias to all the observations
5. Return obs corrected and the average bias.