Add `erfinv` and `erfcinv` for `Float16` and generalize `logerfc` and `logerfcx`

[devmotion]

As the title says :slightly_smiling_face:

I was a bit unsure if computations in erfinv and erfcinv should be performed with Float32 or Float16 since the coefficients in Blair's paper are not representable with Float16.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 72.97297% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 94.10%. Comparing base (c1ce5b1) to head (24b0379). Report is 4 commits behind head on master.

Files	Patch %	Lines
src/erf.jl	72.97%	10 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #372      +/-   ##
==========================================
- Coverage   94.95%   94.10%   -0.85%     
==========================================
  Files          14       14              
  Lines        2914     2935      +21     
==========================================
- Hits         2767     2762       -5     
- Misses        147      173      +26     

Flag	Coverage Δ
unittests	94.10% <72.97%> (-0.85%)	:arrow_down:

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[ViralBShah]

@devmotion Is this good to merge?

[devmotion]

From my side yes but someone has to review it.

[ViralBShah]

Perhaps @oscardssmith ?