feature(render): adds postscript output formats (cli only)

[sverweij]

Description, Motivation and Context

• Adds postscript as an output format
  • ps: PostScript output - see graphviz documentation for ps for details
  • ps2: PostScript output with PDF notations see graphviz documentation for ps2 for details. Will be saved with a .ps extension
• Only available in the command line version

Why? As noted in in #129 postscript might be a reasonable alternative output format for some use cases.

How Has This Been Tested?

• automated non-regression tests & green ci
• additional unit tests
• manual testing

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Documentation only change
• Refactor (non-breaking change which fixes an issue without changing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• 📖

  • My change doesn't require a documentation update, or ...
  • it does and I have updated it

• ⚖️

  • The contribution will be subject to The MIT license, and I'm OK with that.
  • The contribution is my own original work.
  • I am ok with the stuff in CONTRIBUTING.md.

[codeclimate]

Code Climate has analyzed commit b9d7a1f and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (100% is the threshold).

This pull request will bring the total coverage in the repository to 100.0% (0.0% change).

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