Fix #101

[huguesdevimeux]

Fixes #101

The issue was that the lines of NumberPlane were automatically centred on the axis, which could cause problem when x_max was not equal to x_min. (same for y).
Example of the issue :

class Test(Scene):
    def construct(self):
        NPac=NumberPlane(x_max=20).add_coordinates()
        NPac.scale(0.3)
        NPac.center()
        self.add(NPac)

Render this :

As you can see, x-paralleles lines are shifted to the left.
Now, this is fixed :

I tested it with tests set up by #133 (not merged yet) and locally.

I also added a little bit of docstrings.

[PgBiel]

the docs gang strikes again

[XorUnison]

We should also keep in mind that the x/y_min/max values are eventually to be replaced with xRange/yRange (or x_range, however the variable should be called), though I think we should first push this fix, I'll then make an issue for switching to ranges if nothing like that is around yet.

[huguesdevimeux]

@PgBiel Thank you so much Captain Docs ! I did your suggestions. Don't hesitate to check it, if you don't mind. I also thought to add a doc for NumberPlane, but how to do so with all the CONFIG mess ? What to document ?

@XorUnison Why not, but for me x_max is fine. Why do you think it would be better with a range thing?

[huguesdevimeux]

Update : I also fixed a minor bug, when passing a value for faded_line_ratio, the number of faded lines between two non-faded lines was equal to value - 1, which was a bug. I think it was implemented to handle the case when faded_line_ratio is 0, but I don't think this is necessary.

[TonyCrane]

Very effective, this problem has troubled me for a long time :D

[safinsingh]

See comments

[huguesdevimeux]

@safinsingh Fixed, thank you

Addressed