Class CompoundParam

       object --+                
                |                
sip.simplewrapper --+            
                    |            
          sip.wrapper --+        
                        |        
     PyQt5.QtCore.QObject --+    
                            |    
                        Param --+
                                |
                               CompoundParam

Known Subclasses:

• ParamModel
• , jobtasks.JobConfig
• , jobtasks.JobOptions

A collection of Params that itself is a Param. Instances of this class are
used as both descriptors and as return values from the descriptor. This
allows sub-params to be accessed in the most natural way (i.e. param =
container.param, subparam = param.subparam), since the return value of the
first descriptor has the descriptors for the sub-params.

To create a compound param, subclass and add params as class attributes.
Example:

class Coordinate(CompoundParam):
    x = FloatParam()
    y = FloatParam()
    z = FloatParam(4) # Specify default value

Since CompoundsParams are Params, they can also be included within other
compound params:

class Line(CompoundParam):
    startpoint = Coordinate()
    endpoint = Coordinate(x=3, y=2) # specify default value by kwargs

Signal propagation. Executing the following lines:

l = Line()
l.endpoint.x = 5

will result in multiple signals being emitted:
    l.endpoint.xChanged
    l.endpoint.valueChanged
    l.endpointChanged
    l.valueChanged

For any nested param, the change can be detected via either the paramChagned
signal or the generic valueChanged signal. For a top-level param, only the
valueChanged signal will be available.

Compound params can also be serialized to JSON and deserialized from JSON.

WARNING: as descriptors, instances of this class will not behave normally
if used as class variables.