reshape() should return a new copy instead of modifying

[TorokLev]

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reshape modifies the input but numpy doesn't. It would desirable to behave similar.

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It should not break:

const nc::NdArray array = {1,2,3};
std::cout << array.reshape(-1,1).shape();

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[dpilger26]

I disagree, the goal of this library is to be NumPy like, but not necessarily identical. It is more efficient for the default behavior to be an in place reshape and to let the user call the copy() method if they need a copy. I've updated the documentation to be more clear and to reflect this.