Add ac2rc: autocorrelation to reflection coeffs

[phychi]

The results I achieved are the same as those from MATLAB. Unfortunately, ac2rc and ac2poly handle row and column vectors differently, which is reflected in their respective documentation for the same input r. It’s not a bug, but a feature, though it is indeed somewhat counterintuitive. Both functions are implemented by directly calling levinson.

ac2rc: Autocorrelation sequence, specified as a vector or as a matrix. The ac2rc function treats each column of r as a separate channel.
ac2poly: Autocorrelation sequence, specified as a vector or as a matrix. If you specify r as a matrix, ac2poly treats each column of r as a separate channel.
Therefore, the following results are obtained:

>> r = [3, -1, -4, 3, 1, -2];
>> [k, r0] = ac2rc(r)

k =

    0.3333
    1.6250
   -0.4857
   -0.9145
    3.6719


r0 =

     3
    -1
    -4
     3
     1
    -2

>> [k, r0] = ac2rc(r')

k =

    0.3333
    1.6250
   -0.4857
   -0.9145
    3.6719


r0 =

     3