Prepare release of version 4.5.0

[jdebacker]

This PR prepares taxcalc for release of version 4.5.0.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (79cbe02) to head (ac0a329).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2879   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines         2618      2618           
=========================================
  Hits          2618      2618           

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Files with missing lines	Coverage Δ
taxcalc/__init__.py	100.00% <100.00%> (ø)

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