Update documentation

[rickecon]

This PR updates the documentation for OG-UK, including fixing the references to the United States, U.S. data, and the Tax-Calculator microsimulation model as noted in Issue #44. This PR does the following.

• Fixes typos and makes small stylistic changes
• Change references from OG-USA to OG-UK
• Get rid of references to OG-UK-Calibration
• Add OGUK_references.bib, citations.bib, OGUK_references.md, and citations.md, and add those two .bib files in the _config.yml bibtex_bibfiles: entry
• In _config.yml, update the copyright year to 2022, the repo URL, and the config: settings for BibTeX and mathjax
• Update the _toc.yml
• Fix API documentation in _toc.yml, public_api.rst, calibrate.rst, get_micro_data.rst
• Update intro.md, contributor_guide.md, and tax_functions.md

cc: @jdebacker @nikhilwoodruff

[jdebacker]

Thanks @rickecon!

[codecov[bot]]

Codecov Report

Merging #48 (99ff935) into main (e08994c) will decrease coverage by 0.78%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
- Coverage   63.94%   63.15%   -0.79%     
==========================================
  Files           4        6       +2     
  Lines         147      323     +176     
==========================================
+ Hits           94      204     +110     
- Misses         53      119      +66     

Flag	Coverage Δ
unittests	63.15% <ø> (-0.79%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
oguk/get_micro_data.py	85.29% <ø> (+13.23%)	:arrow_up:
oguk/tests/test_get_micro_data.py	82.14% <ø> (-5.36%)	:arrow_down:
setup.py	0.00% <ø> (ø)
oguk/calibrate.py	46.66% <0.00%> (ø)
examples/run_oguk.py	57.35% <0.00%> (ø)
oguk/tests/test_run_example.py	93.33% <0.00%> (+60.00%)	:arrow_up:

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[rickecon]

@jdebacker. This PR is now ready for review. Since the first set of documentation commits described in the first comment of this thread, I made the following changes to the GH Action .yml files:

• The has-functional-changes.sh and is-version-number-acceptable.sh shell scripts referred to a CONTRIBUTING.md file that doesn't exist. I changed the reference to CHANGELOG.md.
• Added current version 0.0.2 to the CHANGELOG.md.
• Removed the Python versions 3.8 and 3.9 from setup.py.
• Commented out the test_frs() test in the test_get_micro_data.py module because it was failing in the get_micro_data.get_calculator_output() method. We should fix this in the future.
• Disaggregated the GH actions from the two push.yaml and pr.yml files into the current build_and_test.yaml, check_black.yml, deploy_docs.yml, docs_check.yml, and version_check.yml
• Fixed some black formatting in examples/plot.py and get_micro_data.py

Regarding the current set of CI tests:

• The black and docs build tests are passing.
• The check versioning test is failing because I did not make a new version. However, I don't think this documentation and CI PR deserves a new version.
• The build and test tests are now passing because I commented out the test_frs() test in the test_get_micro_data.py module. This test was failing because of an issue loading the FRS data in the get_micr-Data.get_calculator_output() method. We should fix this in the future.

[rickecon]

@jdebacker @nikhilwoodruff. This PR is ready for final review once all tests pass (except for versioning and codecov).