Consider supporting Data.Collections from arrays

[jamescasbon]

Currently, in order to create a Data.Collection, you need to pass a list of key, value pairs like so:

var  data = { properties: {...}, items: {...} };

Since this is for tabular style data, you should consider allowing a spec of the form:

var data = { properties: {...}, items: [...] };

This almost works at the moment, except Data.Object presumes a node has a string id in order to do things like ( https://github.com/michael/data/blob/master/data.js#L969 ):

this.html_id = id.replace(/\//g, '_');

Is it really required that all ids are strings? If so, you could support it by using key.toString when you create the graph at https://github.com/michael/data/blob/master/data.js#L1555

Also, would is it not natural to expect a Data.Collection to support index based lookup, such as at?