Add /row/ endpoint support

* option to get index for dataset,
 * API addition, /datasets/[ID] can take an index parameter, if passed the returned dataset will have an index for each row, http://bamboo.io /docs/advanced_commands.html#additional-dataset-query-parameters
* add show, edit, and delete based on index (this is alpha quality, so for now use with caution)
 * API addition, http://bamboo.io/docs/manipulating_data.html#modifying-your-data

Implemented as:
* `get_row(index)`
* `update_row(index, data)`
* `delete_row(index)`

Test for `delete_row()` doesn't count the # of rows as this is currently buggy in bamboo. Instead it tests the availability of the row after deletion.