proposal to solve #78, a solution between numpy and python.

[black-punkduck]

performance on my box:

runtime is 0.012 seconds for female muscle mesh

(using sum method instead of '+' is 3 times longer)

function is only called, when mesh is added. old function was approx 0.001 seconds. Without numpy time is 0.05 seconds, so I think 0.012 is really okay