Add JuliaFormatter

[devmotion]

Same as https://github.com/JuliaStats/GLM.jl/pull/603. I used YAS style to ensure a consistent style throughout JuliaStats.

Closes #299.

Edit: Marking as a draft until the discussion in https://github.com/JuliaStats/StatsFuns.jl/pull/181 is resolved.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.73684% with 24 lines in your changes missing coverage. Please review.

Project coverage is 94.70%. Comparing base (c440511) to head (276140c).

Files with missing lines	Patch %	Lines
src/circular.jl	64.28%	15 Missing :warning:
src/anderson_darling.jl	86.84%	5 Missing :warning:
src/HypothesisTests.jl	83.33%	2 Missing :warning:
src/f.jl	0.00%	1 Missing :warning:
src/permutation.jl	92.85%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #343      +/-   ##
==========================================
+ Coverage   94.52%   94.70%   +0.17%     
==========================================
  Files          29       29              
  Lines        1827     1888      +61     
==========================================
+ Hits         1727     1788      +61     
  Misses        100      100              

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