Update to asynchronous creation

[modelint]

Prompted by an issue raised in the SM Commons, I took a second look at the creation commands and realized that the asynchronous and synchronous creation was ambiguous.

The ambiguous asynchronous creation command was:

Create -> *Folder()

But this could be interpreted as a normal signal to a synchronously created instance:

new folder .= *Folder()
Create -> new folder

Which, after removing the temporary variable reduces to this:

Create -> *Folder()  // Create folder instance synchronously and then send event to it!

So now we specify asynchronous creation with a new symbol like this:

Create *> Folder()

I could have gotten away with:

Create -> Folder()

Here we have a signal directed at a class. (We know it is a class since, if the class model defines a class named Folder it takes priority over any variable. Also, there must be a creation event named 'Create' defined on that class. But that might not be immediately clear to someone reading the action language, so the *> symbol makes it immediately clear that asynchronous creation is happening.

I also added syntax to create multiple instances synchronously. See the relevant section on asynchronous creation.