Support csv backend

[mollerhoj]

I need this feature for my own application.

Notice that we've added an additional "position" attribute, to take advantage of the fact that csvs are ordered.

[coveralls]

Coverage decreased (-0.4%) to 96.619% when pulling 4bcbde5 on mollerhoj:master into f35bb22 on byroot:master.

[sandstrom]

Just a small thought.

Maybe it makes more sense to keep CSV parsing outside this gem? (i.e. closing this without a merge)

There is already support for custom backends, and I'm guessing JSON and YAML is enough for most people.

Also, CSV has no support for data types and parsing them is much harder than JSON or YAML (there is no single CSV specification).

(but I'm no maintainer, so the repo owner obviously decides)

[pironim]

this is nice feature and can be useful on some projects.