Changing meshgrid to mgrid - fixing gdX, gdY and ext_x, ext_y for 2D kCS...

[ccluri]

Fixing issue #6

[parkag]

2D reconstructions for different gdX and gdY look better indeed! However this pull request is not pep8 compliant (lines longer than 80 chars).

It also breaks tests - which means these should be rethought, I believe they are not valid anymore.
The original idea was to test if pykCSD returns the same results as the previous kCSD Matlab scripts.

I think the old tests should be gradually dropped and more unit tests should be added.
This could be a good moment to start it.

[parkag]

To avoid long lines:

        self.space_X, self.space_Y = np.mgrid[
            self.xmin:self.xmax:np.complex(0,nx),
            self.ymin:self.ymax:np.complex(0,ny)
        ]