New interface class AudioEncoder
New interface class AudioEncoder

This class will be the base for new C++ wrapper classes for all
encoders.

BUG=3926
TBR=kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/23999004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@7463 4adac7df-926f-26a2-2b94-8c16560cd09d

sippet/webrtc,krieger-od/webrtc,Alkalyne/webrtctrunk,sippet/webrtc,PersonifyInc/chromium_webrtc,krieger-od/nwjs_chromium_webrtc,sippet/webrtc,aleonliao/webrtc-trunk,krieger-od/nwjs_chromium_webrtc,krieger-od/nwjs_chromium_webrtc,jchavanton/webrtc,sippet/webrtc,aleonliao/webrtc-trunk,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,aleonliao/webrtc-trunk,krieger-od/webrtc,krieger-od/webrtc,PersonifyInc/chromium_webrtc,Alkalyne/webrtctrunk,krieger-od/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,sippet/webrtc,PersonifyInc/chromium_webrtc,aleonliao/webrtc-trunk,krieger-od/nwjs_chromium_webrtc,krieger-od/webrtc,krieger-od/nwjs_chromium_webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,krieger-od/webrtc,Alkalyne/webrtctrunk,PersonifyInc/chromium_webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,sippet/webrtc,PersonifyInc/chromium_webrtc,jchavanton/webrtc,PersonifyInc/chromium_webrtc,krieger-od/nwjs_chromium_webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk