Eq plugin

Initial pull request for the native EQ plugin, #1376 

![image](https://cloud.githubusercontent.com/assets/7412852/5425560/4ecbfbbc-8314-11e4-9a7e-334e7910f87e.png)

> Well, it depends... it can improve accuracy for higher cutoffs, and (I
> think) reduce phase shift... so maybe you could try some kind of "smart
> oversampling" feature, where it's turned on only when the cutoff freq is
> above a certain treshold?

Looks like I need to do some reading up and testing.