Display of float values in husk

[justinethier]

From Rohan Drape. TBD if this change will be made in Husk, but it is worth considering:

i'm wondering how to work around ghc's (i think infuriating)
decisions about when to "show" floats in scientific notation.

ie. "showing" a LispVal that has Float nodes will print 5.0e-2 instead
of the (i think more readable) 0.05.
S.Float x -> Numeric.showFFloat Nothing x ""

ps. there was a haskell-cafe thread about this but it ended at:

http://www.haskell.org/pipermail/haskell-cafe/2013-November/111318.html

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i've made a variant of 'showVal' that works:

  S.Float x -> Numeric.showFFloat Nothing x ""