Add simple :pan control to the sample players.  Example usage I tested with:

;; mono sample
(def kick (sample (freesound-path 2086)))
(kick :pan -1)

and

;; stereo sample
(def sol-do (sample (freesound-path 44929)))
(sol-do :pan 1)
Merge pull request #239 from rogerallen/rallen-pan-sample

Add simple :pan control to the sample players.