Viewer command line support

[Dnyarri]

Update mostly related to Viewer.py and includes minor GUI update and, most interesting, command line support. Now you may use commans like

python viewer.py filename.ppm

to open PPM, PGM and PBM image files.

This release is main version (Python 3.11 and above); corresponding files for Python 3.4 and above are available at 2.20.4.34 tag.

NOTE: This release contain a workaround for Python deprecations, which affected previous release under some circumstances. Previous release of 2.20.4.20 to be deleted.

---

This discussion was created from the release Viewer command line support.

[Dnyarri]

This release contain a workaround for .stat().st_ctime) vs .stat().st_birthtime which are version/platform dependant. Presumably this fix will bring compatibility back, for a price of extra imports.

Note that changes are related to Viewer.py only; PyPNM remains unaffected by these issues since it does not use these methods.