A ParticleEmitter that emits particles within a cone.
Particles will be positioned at the tip of the cone and have initial velocities going towards the base.
    
| Name | Type | Default | Description | 
|---|---|---|---|
angle | 
            
            Number | 
                
                    Cesium.Math.toRadians(30.0)
                
                 | 
            
            optional The angle of the cone in radians. | 
