Customize CSS class names via registerClass arguments.

I find myself wanting to be able to customize my CSS class names.

``` js
var customNamed = Rcss.registerClass({color: 'red'}, 'custom-named');
```

I'm sure this has already been considered. What's the status?

Start at the Rcss.registerClass entry point shown in the issue and inspect how CSS class names are currently generated. Determine the intended behavior for the optional custom name, then verify that named registrations produce the expected class names without breaking existing registrations.

Written by the indexing model from the issue text.