fft_pulse: Calculate the fast fourier transformation for each pulse
In ThierryO/rhinolophus: Identify Bats from Ultrasound Recordings

Calculate the fast fourier transformation for each pulse

1	fft_pulse(pulses, spectrogram, n.fourier = 30)

`pulses`	A list of pulses. E.g. the output of `find_pulses`
`spectrogram`	The spectrogram. E.g. the output of `wav2spectrogram`
`n.fourier`	The number of required Fourier components in each direction.

wav <- read_wav(
  system.file("demo_wav/leislers.wav", package = "rhinolophus")
)
spectrogram <- wav2spectrogram(wav)
pulses <- find_pulses(spectrogram = spectrogram)
pulse.fft <- fft_pulse(pulses = pulses, spectrogram = spectrogram)