DOC: Finalize changes for 4.12 release

[bashtage]

Finish change log for release

[codecov]

Codecov Report

Merging #347 into master will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #347      +/-   ##
==========================================
- Coverage   99.27%   99.14%   -0.13%     
==========================================
  Files          48       46       -2     
  Lines       10961    10785     -176     
  Branches      938      938              
==========================================
- Hits        10881    10693     -188     
- Misses         29       40      +11     
- Partials       51       52       +1

Impacted Files	Coverage Δ
arch/tests/test_compat.py	42.1% <0%> (-57.9%)	⬇️
arch/univariate/recursions_python.py	97.9% <0%> (-0.7%)	⬇️
arch/tests/test_examples.py	92.59% <0%> (-0.52%)	⬇️
arch/tests/utility/test_array.py	99.54% <0%> (-0.01%)	⬇️
arch/tests/univariate/test_mean.py	99.76% <0%> (-0.01%)	⬇️
arch/tests/univariate/test_variance_forecasting.py	99.84% <0%> (-0.01%)	⬇️
arch/tests/unitroot/test_unitroot.py	100% <0%> (ø)	⬆️
arch/tests/utility/test_cov.py	100% <0%> (ø)	⬆️
arch/tests/utility/test_timeseries.py	100% <0%> (ø)	⬆️
arch/tests/univariate/test_moment.py	100% <0%> (ø)	⬆️
... and 8 more

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