add admaNullAngleToCardioidCoeffs

helper script to calculate the weight for weighted adding of front and
back cardioids of a differential microphone array in order to get a zero
at a specified angle
twinMicNullSteering: change fix null sterring

instead of using the notation with beta from Gary Elko, used simple
function to calculate the correct weight to subtract both cardioids.
this allows for angle from 0 to 180 degrees instead of only from 90 to
180 degrees