Some notes on using IDL objects

• Getting started using IDL objects
  A simple example of an object to do an xy plot.

• A simple method for plotting in mulitple windows
  Added a method to update multiple plot windows on one call.

• Customizing objects
  Changing plot parameters after the object has been created. Also reading back values from the object.

• Built-in help
  Adding help so the object can explain how it is used. Also listing the values of internal parameters.