Enhancement: Allow construction of header

[localheinz]

This PR

• allows the construction of the file level header

[codecov]

Codecov Report

Merging #23 into master will decrease coverage by 14.85%.
The diff coverage is 80%.

@@              Coverage Diff              @@
##             master      #23       +/-   ##
=============================================
- Coverage       100%   85.14%   -14.86%     
- Complexity        8       36       +28     
=============================================
  Files             2        8        +6     
  Lines            26      101       +75     
=============================================
+ Hits             26       86       +60     
- Misses            0       15       +15

Impacted Files	Coverage Δ	Complexity Δ
src/Header/Header.php	0% <0%> (ø)	4 <4> (?)
src/Header/Year.php	100% <100%> (ø)	6 <6> (?)
src/Header/Author.php	100% <100%> (ø)	4 <4> (?)
src/Header/Url.php	100% <100%> (ø)	4 <4> (?)
src/Header/CopyrightYears.php	100% <100%> (ø)	6 <6> (?)
src/Header/License.php	100% <100%> (ø)	4 <4> (?)
... and 2 more

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