fix: fft_detector aaps and power law improvements

fix: fit_power_law aaps normalization with dc for correct values of b1

update: remove sources

tidy

fit power law!

add: power law fittting implementation

fix: for issue #4

refactor: tidy and calculate_fft

Merge pull request #3 from Aliqyan-21/dev_azimuthal

update: readme

add: aaps observation doc

add: gnuplot script

feat(FFTDetector): calc_aaps(...) implementation

feat: fftdetector, fft spectrum implementation and visualization of fft spectrum

fix: image markdown