first-try: rename all ``Negate`` to ``NegateFun``
rename Abs and Abs2 to AbsFun and Abs2Fun
revert NegateFun back to Negate
rename Max/Min to MaxFun/MinFun
add `Fun` suffix to Hypot, Atan2
renamed most elementary functors (adding `Fun` suffix)
rename error & gamma functors
renaming for Logit, Logistic, Isfinite, Isinf, Isnan, Xlogx, Xlogy
Allow both Recip and RecipFun, FMA stays as it is
Merge branch 'master' into functor-rename

Resolved conflicts at src/NumericExtensions.jl
Merge pull request #19 from lindahua/functor-rename

Rename Functors