Refactor STEP 3

Not as in love with this refactor as with steps 1 and 2. calc-vert-vel
is mapped to the whole data structure, then vert-gel-in-dive is used
with update-in on each partition’s :dive-points, then assoc-vert-vel is
applied to ordered pairs of dive points. Got to be a cleaner way.
Add Halsey et al to repo