argmin is not the same with numpy

[tomachristian]

NumSharp/src/NumSharp.Core/Statistics/NDArray.argmin.cs

Line 20 in 00d8700

public int argmin(int axis)

this does not look right because it returns int, also np.argmin does not seem to behave correctly (like its numpy counterpart)

[Nucs]

This has been fixed. np.argmin now returns the correct index matching NumPy behavior:

var arr = np.array(new[] { 3.0, 1.0, 2.0, 0.5, 4.0 });
var result = np.argmin(arr);
// Result: 3 (correct index of minimum value 0.5)

Resolved via #600, #602, #603, #596.