Update `mapAccum` docs (and implementation!) (#32)
Update `mapAccum` docs (and implementation!) (#32)

Previously, the `mapAccum` arguments were not in the order one might expect (i.e. the same as other fold-style functions: `function accumulator foldable`). This has been corrected. Furthermore, the documentation contained a formatting error, which has been fixed.
paf31/purescript-behaviors