mnf documentation examples use invalid call signature

[tboggs]

In the following lines of the spectral.mnf doc string, data should be added as the first argument:

>>> denoised = mnfr.denoise(snr=10)

>>> # Reduce dimensionality, retaining NAPC components where SNR >= 10.
>>> reduced = mnfr.reduce(snr=10)

>>> # Reduce dimensionality, retaining top 50 NAPC components.
>>> reduced = mnfr.reduce(num=50)

[aloboa]

Confirm it works with e.g denoised = mnfr.denoise(data,snr=10)