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Extract magic numbers into Constants

See:
https://sourabhchablog.wordpress.com/2013/10/07/code-smell-of-the-week-magic-numbers/
and
http://stackoverflow.com/questions/47882/what-is-a-magic-number-and-why-is-it-bad

The main reason I'm doing this refactoring is to get a better idea of
what the code is doing before I move in for deeper refactors.

The nice thing is this extraction highlights a bunch of duplication in
intent. Perhaps instead of passing in an array (which uses numbers to
retrieve the values) we could use an object (which allows us to look up
values in it with a meaningful name)
Extract coordinate translation for the L command

I've noticed there's a series of functions that do the same basic thing
(changing the value of the coordinate variable in some way) so I'm
extracting functions which conform the the same interface:

newCoordinate = translationFn(coordinate)

While this leaks knowledge of how coordinates exist into a function it
let's us begin to collapse the complexity  of the marsRover's move
function.

These translationFns will live on the translations map. This
conveniently allows us to look up a function based upon the command that
was passed in.
Extract right translation

We're beginning to see some payoff from the translations map.  You'll
notice we've been able to eliminate an else if. Plus we have 1 fewer
call to xyCoordinates and the console.log.
Introduce parameter for detectObstacle

The forward/backward translation is a bit too large to tackle right this
instant; so I'm breaking out the logic for detecting an obstacle first.

By removing obstacleDetection as a responsibility of the
Forward/Backward function and placing it in the general move section I
make it simpler to extract the forward/backward into a translationFn