Evaluate existing C++ numpy implementations

[carlkl]

evaluate existing C++ numpy implementations

I propose to evaluate existing C++ numpy-like implementations for #202

There are existing implementations, see:

• xtensor
• NumCpp
• NdArray-Cpp and others

xtensor is maybe a little bit heavy for the use case. NumCpp is limited to 2D arrays. However NumCpp is a header only C++ implementation and can be configured with 'NUMCPP_NO_USE_BOOST' to avoid Boost and thus any further dependancies.

All other numpy-like libraries I found seems to be in an very early state.