Release 4.0

[palday]

• update README (should be easy to adapt highlights from NEWS or maybe just drop the new major release bit and add a reference to NEWS)
• run JuliaFormatter
• create a new branch from current main called 4.x (after merging)

@dmbates do you want to take care of the formatting? done!

[codecov]

Codecov Report

Merging #540 (1032d5b) into main (680aec4) will decrease coverage by 0.04%.
The diff coverage is 94.82%.

@@            Coverage Diff             @@
##             main     #540      +/-   ##
==========================================
- Coverage   94.49%   94.44%   -0.05%     
==========================================
  Files          27       27              
  Lines        2414     2468      +54     
==========================================
+ Hits         2281     2331      +50     
- Misses        133      137       +4     

Impacted Files	Coverage Δ
src/linalg.jl	62.82% <68.75%> (+0.97%)	⬆️
src/Xymat.jl	87.50% <81.81%> (ø)
src/schema.jl	80.00% <83.33%> (ø)
src/varcorr.jl	98.27% <87.50%> (-1.73%)	⬇️
src/arraytypes.jl	94.33% <90.00%> (ø)
src/utilities.jl	96.87% <90.00%> (+0.04%)	⬆️
src/mixedmodel.jl	91.48% <91.66%> (ø)
src/randomeffectsterm.jl	96.10% <91.66%> (-1.12%)	⬇️
src/remat.jl	96.70% <93.67%> (+0.06%)	⬆️
src/bootstrap.jl	97.84% <94.11%> (ø)
... and 17 more

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[dmbates]

• This looks good to go for me whenever you are satisfied.

• I think that running the code through the formatter was a good idea. Thanks for doing that. In some ways consistency of style is more important than the particular style being used.