Many functions in turbulence submodule broken on pip install

Any of the submodules that try to import wetb.wind.turbulence.spectra are broken on a pip install. This is because the mann_spectra_data.npy file is not included in the install, so there is a FileNotFoundError when it tries to load the numpy file and fails. If you clone and install locally, the functions work just fine.

cc @mmpe