[GSoC] Dataframes for D

[bachmeier]

Looking at the readme, I see the following example for accessing 
elements by name:

df[["1"], ["0"]];

Why can't that instead be

df["1", "0"];

Something that gets in the way of adoption is verbose notation, 
and I'm not seeing any advantage to the array notation.

Also, for this example:

Index indx;
indx.setIndex([1, 2, 3, 4], ["Row Index"], [1, 2, 3], ["Column 
Index"]);

That's pretty verbose/hard to parse compared to

rownames(x) = [1, 2, 3, 4];
colnames(x) = [1, 2, 3];