An Efficient Full-Band Sliding DFT Spectrum Analyzer

[jurihock]

The oSDFT seems to be performing better than the current mSDFT:

• It's definitely faster (not much, but still)
• It's less noisy (assuming there are no bugs)
• It's easier to implement (at least in Python using Numba)

I'm considering to replace the mSDFT with oSDFT and dropping the C implementation. The current mSDFT implementation will be moved to an archive branch.