Adapt documentation to version 0.10.0

[DunklesArchipel]

Checklist

• [x] Added an entry in doc/news/.
• [x] Added a test for this change.
• [x] Updated the documentation.

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This PR adds an almost complete documentation of the svgdigitizer module. The examples in the documentation are all executed and thus serve as additional tests to the module.

Linkchecker will fail since some links point to content in the repository which is included in this PR. These issues must be addressed in a subsequent PR.

I experienced several issues with byexample testing the readme. These have to be addressed also separately (see #187).

TODO:

• [x] CLI flag --si-units

  Fixes #17 Fixes #119 Fixes #167 Fixes #177

[DunklesArchipel]

Disable `byexample' in the tests (see #187)

[DunklesArchipel]

We merge this without further review. Feel free to add suggestions as PR or issues. :)