ENH: new preprocessing / FFT tutorial example
ENH: refactor example + address discussion

COSMITS
ENH: fixes + addresses discussion

COSMITS

COSMITS
ENH: add compute_epochs_pds + refactor example
COSMITS
FIX debugging changes
update whats new
update reference
ENH: address discussion
ENH: add parallel + address discussion
COSMITS/DOC
ENH: address discussion
Merge pull request #604 from dengemann/fft_spectra

[MRG]: new preprocessing / FFT tutorial example