Implemented Yule-Walker VAR model fitting
streamlined VAR tests
updated years
switched to scipy solver
FIX: removed syemmtry assumption
FIX: wrong coefficient step size
ENH: Yule-Walker covariance estimation
FIX: added test for COH <= 1
ENH: skipping incorrect resudals from cov
ENH: improved spectal estimation
fixed scipy solving/fft
improved tests
fixed test
Merge pull request #23 from kazemakase/yule-walker

ENH: Yule walker VAR model fitting