Refactor dive datastructure

Big refactor.
Before: three lists - dive points, dive stats, elements
After: one list partitioned into dives. Each dive is a hash with the
descriptive stats, list of points, and list of elements.
Add trace dependency

For debugging
Some useful commands

Because searching through REPL history is tiring
Data structure evolution through steps

Because it’s hard to keep this straight in your head all the time