Raise limit on zoom to 25600% so manual zoom can be higher. Refs #137

* Still leaving some upper limit so that typos don't result in a zoom
  level of something crazy.
* This also allows 'fit to texture' to zoom in more, but I'm OK with
  that.

renderdocui/Windows/TextureViewer.cs

@@ -2093,7 +2093,7 @@ namespace renderdocui.Windows
 
             float prevScale = m_TexDisplay.scale;
 
-            m_TexDisplay.scale = Math.Max(0.1f, Math.Min(8.0f, s));
+            m_TexDisplay.scale = Math.Max(0.1f, Math.Min(256.0f, s));
 
             FetchTexture tex = CurrentTexture;