Make pynacl optional dependency

disco/voice/client.py

@@ -3,7 +3,10 @@ import socket
 import struct
 import time
 
-import nacl.secret
+try:
+    import nacl.secret
+except ImportError:
+    print 'WARNING: nacl is not installed, voice support is disabled'
 
 from holster.enum import Enum
 from holster.emitter import Emitter

requirements-optional.txt

@@ -0,0 +1 @@
+pynacl==1.1.2

requirements.txt

@@ -4,4 +4,3 @@ inflection==0.3.1
 requests==2.13.0
 six==1.10.0
 websocket-client==0.40.0
-pynacl==1.1.2