`find-replacement-lessons-within-time` - use destructuring for arg
`find-replacement-lessons-within-time` - use destructuring for arg

Something we picked up from:

    http://blog.jayfields.com/2010/07/clojure-destructuring.html

after wondering if we could do what we did in this patch. The answer is
yes =)

We'll be making use of this technique a lot after the major refactorings
are completed.

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods