Unit test image, line and pdf document

[johnfercher]

Description

• Fix cov and linter files to only work in real code;
• Update unittests example with line;
• Add more fixtures;
• Unit test image package: bytesImage, fileImage and fromBytes;
• Unit test line package;
• Rename orientation string type;
• Improve saving of pdf;
• Unit test pdf document;
• GoDoc on line props;
• Unittest the test package;
• Add more test/maroto jsons.

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

All modified lines are covered by tests ✅

❗ No coverage uploaded for pull request base (v2@62f4191). Click here to learn what that means.

Additional details and impacted files

@@          Coverage Diff          @@
##             v2     #334   +/-   ##
=====================================
  Coverage      ?   44.11%           
=====================================
  Files         ?       42           
  Lines         ?     1451           
  Branches      ?        0           
=====================================
  Hits          ?      640           
  Misses        ?      792           
  Partials      ?       19           

Flag	Coverage Δ
unittests	44.11% <0.00%> (?)

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