When attempting to access array values via the `json` resource:
```
describe json('/tmp/test.json') do
its(['array',0]) { should eq "zero" }
end
```
... the resulting data would be an array of the size of the original array
with all the values replaced with nils:
```
expected: "zero"
got: [nil, nil, nil]
```
This was due to a bug in the ObjectTraverser mixin that mapped array values
back through `extract_value` rather than properly handling the passed-in
key(s). This worked fine for the specific data format created by the `csv`
resource but did not work `json` or any other resource that subclassed the
`JsonConfig` resource.
This change fixes the logic when dealing with an array when it's encountered,
and fixes up the `csv` resource with its own `value` method.
This change also adds tests for ObjectTraverser.
Signed-off-by: Adam Leff <adam@leff.co>
