time series

[Jason Stover]

Does anyone mind if I start adding some time series
routines to src/math? I know I mentioned writing a neural
network procedure before, but I have a more urgent need
for time series models. 

I would also move src/math/linreg/coefficients* up one
level to its own directory. I think this would be a good
idea, given that so many statistical procedures (including
those for time series) need coefficient data structures. They
aren't specific to regression.

-Jason