Clarify shadow DOM algorithms

[kjax]

My group has found shadow DOM spec to be confusing about the order that the slotting and flattening algorithms are applied. Is each step applied to all of the nodes before continuing to the next step?

Perhaps changing to this statement:
The slotting algorithm must be used to determine the assigned slot for each node and must be equivalent to processing the following steps

[hayatoito]

Thank you for the suggestion!

[hayatoito]

I have also made the Flatting Example more readable at b8567cf

If you have any other idea which make the spec understandable, I appreciate it. Any minor fixes are welcome.