mrv2 v0.6.4

v0.6.4

• Improved Python plug-in API. Now plug-ins are defined with a base class,
  and menus with a dict (without tuples) like:

      class HelloPlugin(mrv2.plugin.Plugin):
          def hello(self):
              print("Hello from plug-in!")

          def menus(self):
              menus = { "New Menu/Hello" : self.hello }
              return menus

• You can have multiple plug-ins in a single .py and have the class be named
  whatever you like, as long as you derive from mrv2.plugin.Plugin.
• Improved the look of Gamma, Gain and Volume sliders.
• Fixed Window on Top check mark when run from the Context menu.
• Fixed Presentation mode not returning to its previous state when switched off.
• Fixed an internal OpenGL error.
• Fixed Playback menu status at the beginning when Auto Playback was checked.
• Fixed pixel color look-up when loading a single frame.