use permute instead of reshape
wave vector calculation in separate function
add test of input arguments

Frequency vector can be row or column vector.
add function for near field beamsteering
add function to multiply 3D arrays

It does a normal matrix multiplication along the first two dimensions
and "broadcasts" this operation along the third dimension without using
loops.
bugfix
add function for coherence matrix in nearfield
bugfix

MVDR scaling coefficient was missing.
fix incomplete error message
fix tests

Used old function name.
include nearfield beamforming