Add unit tests for functions in WindField folder

[ufechner7]

To ensure that the translation of this code into Julia is correct, we need unit tests.

First set needed for the function getWindDirT

• Direction_Constant
• Direction_Constant_wErrorCov
• Direction_Interpolation
• Direction_Interpolation_wErrorCov
• Direction_InterpTurbine
• Direction_InterpTurbine_wErrorCov

And for the function getWindDirT_EnKF

• Direction_EnKF_InterpTurbine
• Direction_InterpTurbine_wErrorCov

And for the wind shear

• Shear_Interpolation
• Shear_LogLaw
• Shear_PowerLaw