Fix Sabelhaus-Song variances

[Mv77]

I made a grave error with the calibration tools. Sabelhaus & Song's model returns income shock variances, while HARK expects standard deviations. I did not transform the variances and thus, at the moment, shock variances are being interpreted as standard deviations. This can cause income uncertainty to be understated by a factor of 10.

This PR fixes the error. My sincerest apologies for this bug and its timing.

• Tests for new functionality/models or Tests to reproduce the bug-fix in code.
• Updated documentation of features that add new functionality.
• Update CHANGELOG.md with major/minor changes.

[codecov-io]

Codecov Report

Merging #980 (05e6446) into master (799943e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #980   +/-   ##
=======================================
  Coverage   71.85%   71.85%           
=======================================
  Files          62       62           
  Lines        9205     9205           
=======================================
  Hits         6614     6614           
  Misses       2591     2591           

Impacted Files	Coverage Δ
HARK/Calibration/Income/tests/test_IncomeTools.py	100.00% <ø> (ø)
HARK/Calibration/Income/IncomeTools.py	92.79% <100.00%> (ø)
...nsumptionSaving/tests/test_IndShockConsumerType.py	100.00% <100.00%> (ø)
...ptionSaving/tests/test_IndShockConsumerTypeFast.py	100.00% <100.00%> (ø)

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[llorracc]

Oops! Thanks for catching it -- just in time, we haven't released 0.10.9 yet, but are hoping to do so tonight or tomorrow.

PS. Maybe you don't need to update the changelog because you had updated it already with your earlier PR? If that's right, just tick off the "changelog" tick box, and I'll merge.

[Mv77]

That's great to hear. Yes, the tools were already in the changelog. I have simply added a link to this PR. It can be merged after tests complete (although they should pass).

Thank you and sorry again!

[Mv77]

All tests passed, this can now be safely merged!