BUFFER property stores output in Z-buffer.
  - ::Draw switches to Z-buffer on each call.
  - ::ResizeDrawWidget renamed to ::Resize.
      * Resize all types of devices (even those that do not support windows).
  - ::Save switches to Z-buffer for non-IM raster files.
  - Added ::ShowBuffer method.
  - ::SetCurrent checks if windows are supported.
  - ::Init does not create windows when BUFFER is set.
  - MrSaveAs checks if windows are supported
  - Output file name set properly
Merge branch 'master' of https://github.com/argallmr/mrwindow