Add tc --outdir option

[martinholmer]

This pull request adds an --outdir option to the tc command-line tool as requested in issue #1794.

[codecov-io]

Codecov Report

Merging #1801 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1801   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          37      37           
  Lines        3042    3061   +19     
======================================
+ Hits         3042    3061   +19

Impacted Files	Coverage Δ
taxcalc/taxcalcio.py	100% <100%> (ø)	⬆️

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