Add footer and header tests

[johnfercher]

Description

• Update docs
• Add unit tests for Header and Footer.

Related Issue

#386

Checklist

check with "x", ONLY IF APPLIED to your change

• All methods associated with structs has func (<first letter of struct> *struct) method() {} name style.
• Wrote unit tests for new/changed features.
• Followed the unit test when,should naming pattern.
• All mocks created with m := mocks.NewConstructor(t).
• All mocks using m.EXPECT().MethodName() method to mock methods.
• Updated docs/doc.go and docs/*
• Updated example_test.go
• Updated README.md
• Executed make examples to update all examples inside docs/examples.
• New public methods/structs/interfaces has comments upside them explaining they responsibilities
• Executed make dod with none issues pointed out by golangci-lint

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.05%. Comparing base (2005114) to head (fe76cf4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #432      +/-   ##
==========================================
+ Coverage   81.90%   84.05%   +2.15%     
==========================================
  Files          61       61              
  Lines        2099     2099              
==========================================
+ Hits         1719     1764      +45     
+ Misses        350      308      -42     
+ Partials       30       27       -3     

Flag	Coverage Δ
unittests	84.05% <ø> (+2.15%)	⬆️

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