1. Extract the source code of gaussian_kde from Scipy and add it
	- Add `print` to each step for debug, thus i can know the detail of
	  gaussian_kde
	- Find the difference between my version and theirs

TODO:

	Why the energy is `diff*tdiff`, without square as Gaussian Function
	is :

			g(x) = A*exp(-(x-miu)^2/2*sigma^2)

	???

	In which:

		diff = x-miu
		tdiff = 1/2*(sigma^2)*(h^2) -- h is bandwidth