The fourier transform now disregards the last onset of a sequence tha…

[Jellevanderwerff]

Addresses #74 .

The problem before was that sequences that do not end with an interval contain a final onset, while the Fourier transform should be based on intervals. As such, when the FFT is performed there's artifacts of this final onset.

We now disregard the final onset and only consider the intervals. A note was added to the documentation about htis.