WIP: New effects added

After figuring out how to compile effects I've managed to add the
following:

  * Band Pass Filters (`:bpf`, `:rbpf` and `:nrbpf`)
  * Ring Modulation (`:ring_mod`)
  * Chorus (`:chorus`)
  * Harmoniser (`:harmoniser`)

The inspiration for the synth designs was taken from these sites:

  - (bpf) - adapted from existing implementations
  - (ring mod) http://ecmc.rochester.edu/ecmc/docs/supercollider/scbook/Ch21_Interface_Investigations/ixi%20SC%20tutorial/ixi_SC_tutorial_06.html
  - (chorus) https://soundcloud.com/nathaniel-virgo/supercollider-tweet-from-4
  - (harmoniser) http://comments.gmane.org/gmane.comp.audio.supercollider.user/18982

To use these in SP you'll need to uncomment them in synthinfo.rb in the
`@synth_infos` collection.
Merge pull request #174 from xavriley/new_effects

WIP: New effects added