nc::append should be able to operate empty NdArray<> too.

[TorokLev]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

In Python it looks like this:

collector = np.array([])
np.append(collector, 3)

it should look similar in C++

#include <NumCpp.hpp>
nc::NdArray<double> collector;
nc::append( collector, {3});

but it breaks since collector is empty.

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[TorokLev]

This applies to stack, vstack and hstack too.

[dpilger26]

Implemented as part of release version 2.11.0.