Reshape consistency fix

[darkestpigeon]

What?

Fixing a bug with reshape, where it mistakes a non-contiguous C layout for contiguous F layout (see issue #660).

Why

A simple illustration why this is a problem:

import arraymancer

let x = arange[float](0, 6).reshape(2, 3).permute(1, 0) # has shape [3, 2] and is not C-contiguous (but is F-contiguous)
let y = x.reshape(3*2).reshape(3, 2) # the reshapes shouldn't change the contents

echo x
echo y
doAssert x == y

Right now this assertion fails.

How

The check for whether the tensor is F-contiguous is removed. No-copy reshape is only performed if the tensor is C-contiguous.