Add all-your-base exercise

[haus]

This commit adds the all-your-base exercise, with the tests ported from
the ruby version of the exercise.

[yurrriq]

Hey, thanks! First, I think you'll need to rename all_your_base.clj to example.clj to get the tests passing. And then I think it'd be good to keep the function arguments on one line instead of one per argument, e.g.

[x y z]
;; instead of
[x
 y
 z]

[yurrriq]

The (->> ...) form in the :else clause of convert's cond looks misaligned, at least on mobile, so maybe double check that too and reindent as necessary.

[haus]

Thanks for the quick feedback. I pushed out a commit that should resolve it. Happy to squash that into the previous commit if travis passes.

[yurrriq]

LGTM, thanks!