This commit includes a blind frequency correction mechanism for FM
signals. It uses the information of the angle difference between two
concecutive samples and a VCO to continuously compenstate any frequency
offset. To avoid intermodulations, a low pass filter is used trying to
pass only the DC component that is needed.
* Switch from amplitude based approach to auto-correlation
* Limit the bandwidth of the PLL using a low pass filter
* Reject noise of the PLL using a very steep low pass after it