Ship survey datasets

[leewujung]

Similar to #42, some Echoshader functionalities involve data from mobile platforms such as ships. Let's use the Pacific hake survey data for prototyping purposes.

This echopype-examples notebook is a good resource to get started. Using data from the date range 20170720 - 20170806 will give data from an entire "leg" of the survey, which is a good target for interactive processing.

Detail of data access is in the notebook.

[leewujung]

Now that there are organized datasets and the notebook used to generated them in #92, we can close this issue!