Make CopyingTable into a separate function

[hyanwong]

This allows us to show a copying table without making a TreeInfo class, which is useful with the final tree sequence. It also cuts down on the number of lines of code, even with the extra test. You can call the new class as e.g.

sc2ts.info.CopyingTable(ts, node_id).html

[jeromekelleher]

Looks good, and this is definitely a help. I don't see why it's a class though, when all you access from the return value is the html attribute? Might as well make it

def copying_table(ts, ..):

    return html

[hyanwong]

I'm using the class to keep the various functions grouped together: I lose track of them when all stuck at the top level.

I just reworked slightly to make it clearer. The html() method now just does the formatting, and the init one sets up the necessary arrays etc, which makes it cleaner to output different formats for the same node copying table.