Make format program and arguments configurable

[expipiplus1]

If this needs any changes, then someone else will have to take it over the line, putting this up here just in case.

[regen100]

Could you resolve the conflicts in your PR?

[expipiplus1]

merged, looks like it was just get_document -> get_text_document

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.30%. Comparing base (890bb77) to head (972bf73).

:exclamation: Current head 972bf73 differs from pull request most recent head e142bf9

Please upload reports for the commit e142bf9 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
- Coverage   93.04%   92.30%   -0.74%     
==========================================
  Files           3        2       -1     
  Lines         345      338       -7     
==========================================
- Hits          321      312       -9     
- Misses         24       26       +2     

Flag	Coverage Δ
unittests	92.30% <100.00%> (-0.74%)	:arrow_down:

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