Create a base class for assemblers.

This base class defines an interface that assemblers must adhere to.
For now, we use it to hold the code buffer.

Change-Id: I487430bb98c7044e57b348cffa1e74a2a4c8026f
diff --git a/src/code-buffer-vixl.h b/src/code-buffer-vixl.h
index 3fdfa22..d345805 100644
--- a/src/code-buffer-vixl.h
+++ b/src/code-buffer-vixl.h
@@ -1,4 +1,4 @@
-// Copyright 2014, VIXL authors
+// Copyright 2016, VIXL authors
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -39,7 +39,7 @@
   static const size_t kDefaultCapacity = 4 * KBytes;
 
   explicit CodeBuffer(size_t capacity = kDefaultCapacity);
-  CodeBuffer(void* buffer, size_t capacity);
+  CodeBuffer(byte* buffer, size_t capacity);
   ~CodeBuffer();
 
   void Reset();