Add support for ANSI styled text

[DavidGregory084]

Fixes #76

TODO:

• Decide whether to add rendering options to omit ANSI codes
• Decide whether to attempt some kind of ANSI feature detection Nope too complicated
• Add Doc tests for more complex usage of DisplayStyles
• Add tests for Attrs
• Add Javadocs to new code
• Implement Object methods properly for new Doc subtypes
• Find a more efficient way to deal with the Attrs stack (see e.g. Haoyi's post about micro-optimizing fansi)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.90722% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 97.78%. Comparing base (fb37e2e) to head (03e0083).

Files	Patch %	Lines
...va/com/opencastsoftware/prettier4j/ansi/Attrs.java	92.59%	1 Missing and 5 partials ⚠️
...main/java/com/opencastsoftware/prettier4j/Doc.java	94.18%	4 Missing and 1 partial ⚠️
...a/com/opencastsoftware/prettier4j/ansi/Styles.java	98.80%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##               main      #77      +/-   ##
============================================
- Coverage     98.15%   97.78%   -0.38%     
- Complexity       51      211     +160     
============================================
  Files             1       10       +9     
  Lines           271      632     +361     
  Branches         63      109      +46     
============================================
+ Hits            266      618     +352     
- Misses            1        6       +5     
- Partials          4        8       +4     

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