Functions for harmonisation

[gerritholl]

Function 1 takes

• vector of fundamental calibration parameters
• vector of observations Outputs:
• vector of brightness temperatures or radiances

This function does NOT output uncertainties, or sensitivities.

Function 2 takes same input as function 1.

Outputs: sensitivities ∂R_e/∂a_0, ∂R_e/∂C_S

Function 3 takes the same inputs.

Outputs: expected error correlation between two observations within the same sensor, but only considering the effects that are not fully systematic, because fully systematic uncertainty is treated individually (see #22). This can be read either directly from the effects table, or needs to combine different effects that feed into a particular variable.

[gerritholl]

I don't think this is required anymore. @shunt16 can you clarify if this is still needed? I know that @octoflar does not need it.