matched filter improved.

[pravirkr]

Matched filter:

• Astropy kernels are not helpful. Now, custom kernels are used, which gives more control over normalization.
• Astropy convolve_fft is too complicated. We need a simple FFT-based convolution, so using numpy FFT functions with numba (rocket-fft).
• In principle, this is based on spyden. Templates are also mean-subtracted to remove bias. Hopefully, this is correct!
• It will be useful for the pulsar module + upcoming simulation module.