Fix multiple problems in Erf and InvErf methods

[takano-akio]

This pull request fixes errors in normcdf, inverf, inverfc and invnormcdf.

normcdf

By definition, normcdf = (/2) . erfc . negate . (/sqrt 2). However,

Prelude Numeric.AD Data.Number.Erf> diff ((/2) . erfc . negate . (/sqrt 2)) 1
0.2419707245191434
Prelude Numeric.AD Data.Number.Erf> diff normcdf 1
-0.3961674381354548

inverf etc.

inverf . erf and erf . inverf should be both identity functions (within their domain), so their derivative should be const 1. However,

Prelude Numeric.AD Data.Number.Erf> diff (inverf . erf) 1
0.7483717940991074
Prelude Numeric.AD Data.Number.Erf> diff (erf . inverf) 0.4
0.8235235351131942

There are similar issues with inverfc and invnormcdf.