Enhancement: Add Header

[localheinz]

This PR

• adds Header

[codecov]

Codecov Report

Merging #34 into master will increase coverage by 0.13%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #34      +/-   ##
============================================
+ Coverage      98.6%   98.73%   +0.13%     
- Complexity       50       53       +3     
============================================
  Files            12       13       +1     
  Lines           143      158      +15     
============================================
+ Hits            141      156      +15     
  Misses            2        2

Impacted Files	Coverage Δ	Complexity Δ
src/Header.php	100% <100%> (ø)	3 <3> (?)

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