Math without margin applying value responsibility

[johnfercher]

Description

• Remove responsibility of math applying margins
• Move margins applying responsibility to bar, qr, matrix and image.
• Start unit tests of math

Related Issue

Checklist

check with "x", if applied to your change

• All methods associated with structs has func (s *struct) method() {} name style.
• Wrote unit tests for new/changed features.
• Updated docs/doc.go
• Updated pkg/pdf/example_test.go
• Updated README.md
• Updated all examples inside internal/examples
• New public methods/structs/interfaces has comments upside them explaining they responsibilities
• Executed make dod with none issues pointed out by golangci-lint and goreportcard-cli

[codecov]

Codecov Report

Patch coverage: 38.99% and project coverage change: +2.61% 🎉

Comparison is base (d38470c) 23.56% compared to head (4a6d56c) 26.16%.

Additional details and impacted files

@@            Coverage Diff             @@
##               v2     #313      +/-   ##
==========================================
+ Coverage   23.56%   26.16%   +2.61%     
==========================================
  Files          20       20              
  Lines         968      971       +3     
==========================================
+ Hits          228      254      +26     
+ Misses        734      710      -24     
- Partials        6        7       +1     

Flag	Coverage Δ
unittests	26.16% <38.99%> (+2.61%)	⬆️

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

Files Changed	Coverage Δ
internal/code.go	0.00% <0.00%> (ø)
internal/image.go	0.00% <0.00%> (ø)
internal/math/math.go	53.85% <51.12%> (+49.93%)	⬆️

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