Link tests against std math libs.

For some reason this isn't required on OS X...
Turbo speed! Enable optimisations on x86 family CPUs.

Also updating copyright notices on CMake scripts.
Move track_correlate into its own file where other correlators can live too.
Rename loop filter diagram, its really first order.
Get rid of calc_loop_coeff, we want gains not taus.
Updates to the calc_loop_gains function, the math was/is a bit wrong.

The implementation is now equivalent to the old calc_loop_coef function but the documentation is still incorrect.
Updating discriminator functions and adding simple first order loop filter implementation.