createCommand(func, canExecute)
        Create a Command from a given function, for use with ViewModels.
A Command is a function with an extra 
    
    
    
    
    
        
canExecute observable property to determine
whether the command can be executed.  When executed, a Command function will check the
value of canExecute and throw if false.  It also provides events for when
a command has been or is about to be executed.
    | Name | Type | Default | Description | 
|---|---|---|---|
| func | function | The function to execute. | |
| canExecute | Boolean | true | optional A boolean indicating whether the function can currently be executed. | 
