Improve the jsoc client.

* Add the abilty to specify Segment as an attr.
* Add documentation to the Attributes.
* Fix the docstrings for JSOCClient to make them reflect the new API.
* Rename JSOCClient.jsoc_query to JSOCClient.query.
small typo
Merge pull request #4 from CyclingNinja/JSOC_query

Improve the jsoc client.