Shift to modules

[jbisits]

The two code scripts are not that related and potentially load things that a user may not want. Reworking the scripts into modules will allow an individual part of the package, and the exported functions, to be accessed without need to have the whole (admittedly not huge..) package.

[jbisits]

Whilst doing this it might be nice to add a simple module that can find specific parts of the Ocean. For example, a function southern_ocean that returns a Raster data structure that is the Southern Ocean only.