vcf_plugins: vcf_plugins (LADSPA equalizer plugins)

LADSPA plugins for audio EQ biquad filters based on the cookbook
formulae by Robert Bristow-Johnson.

The following filters have been implemented:
    * Two low pass filters
    * High pass filter
    * Two band pass filters
    * Notch filter
    * Peaking EQ filter
    * Low shelf filter
    * High shelf filter
