LPC burg: ar_burg() interface - returns reflection coeffs - same as …

[oyd11]

…matlab call as well, lpc() - call - returns 2 params - same as Levinson version

[oyd11]

Hi, I wrote the function @staticfloat integrated here before (see: https://github.com/JuliaDSP/DSP.jl/pull/156 ) - this is great, but to be able to use this version in my own code - I also need the Reflection-Coefficients as a return value (they can be re-evaluated - but there's a numerical stability cost) I've wrapped the lpc() call in a unified interface - just like Static did, but provided a 'ar_burg()' function call with the specific Burg algorithm which includes the Reflection-Coefficients as a side effect. This is the same as the Matlab "arburg()" call [ https://www.mathworks.com/help/signal/ref/arburg.html ], feel free to remove the extra dash (now that I see that Matlab doesn't have that.

[oyd11]

note: the non passing CI test seems to be due to some non-related incompatibility issue with Julia nightly (0.7 line) - something about some functions to have moved out of base into DSP

[wheeheee]

Superseded by #517, although more tests e.g. for FixedPoint types could be added.