Get rid of Numpy dependency

[yayachiken]

We only need Scipy to apply a low-pass filter to the Morse stream. Otherwise, we would get nasty clicks whenever the carrier is switched on or off.

This introduces quite a bit of bloat. In addition, we need only a very primitive low-pass filter. Reimplementing this would get rid of this more or less useless dependency.

(Note: We also use Numpy for convenience, we could get rid of this as well.)

[yayachiken]

Note to self: An exponential dropoff at the beginning and end of the carrier pulse would work already. (At least this is part of a question on the German Ham radio license exam...)

Would need to experiment a bit with the timings when I have more time.

[yayachiken]

Progress: Got rid of Scipy dependency, now only Numpy remains.