Added support for changing the volume of RTCAudioSource as discussed in BUG=webrtc:6533
This is a short term solution to change the volume of a RTCAudioTrack (which contains an RTCAudioSource property) until applyConstraints for RTCMediaStreamTracks has been implemented.
This CL adds one new Objective-C method to AudioSourceInterface's wrapper: -(void)setVolume:(double)volume

BUG=webrtc:6533, webrtc:6805

This is my first CL for Chromium/WebRTC, so please let me know if I did something wrong.

Review-Url: https://codereview.webrtc.org/2534843002
Cr-Commit-Position: refs/heads/master@{#16809}
diff --git a/AUTHORS b/AUTHORS
index 4ff9c39..a1c8a67 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,4 +1,4 @@
-# Names should be added to this file like so:
+# Names should be added to this file like so:
 # Name or Organization <email address>
 
 Adam Fedor <adam.fedor@gmail.com>
@@ -13,9 +13,9 @@
 Cody Barnes <conceptgenesis@gmail.com>
 Colin Plumb
 Eric Rescorla, RTFM Inc. <ekr@rtfm.com>
+Frederik Riedel, Frogg GmbH <frederik.riedel@frogg.io>
 Giji Gangadharan <giji.g@samsung.com>
 Graham Yoakum <gyoakum@skobalt.com>
-Hugues Ekra <hekra01@gmail.com>
 Jake Hilton <jakehilton@gmail.com>
 James H. Brown <jbrown@burgoyne.com>
 Jiawei Ou <jiawei.ou@gmail.com>