Windows: product names, the editors, WSL; the Linux page's image step

Assembled from development commit c3c40f6c8fca. Since 830b193: on Windows the
products carry Windows names (ktext.exe, klammertext.dll, document.dll,
reflect.dll) and the console's output code page is UTF-8 for a run; the
editor tooling works on Windows (VS Code, Sublime Text, Vim, with the
interpreter's name chosen by platform) and Notepad++ joins it
(doc/edit/notepadpp: a User Defined Language and two Run-menu commands);
a sixth install page, doc/install/windows_wsl_install.md, for Linux
inside WSL; the Windows page opens with the three routes and gains its
editor section, the PowerShell quoting and Path notes; the Linux page
installs OpenImageIO from the python3-openimageio package and verifies
with kdiag --machine; the README lists all six install pages. Linux and
macOS behaviour is unchanged.

doc/edit/sublime/README.md

@@ -203,8 +203,8 @@ elsewhere) are not part of this package, but they exist: the **Klammertext
 language server** (`doc/edit/shared/klammertext_ls.py`, the same program the
 VS Code extension uses) serves them to Sublime through the community LSP
 package.  Install "LSP" from Package Control and add a client with
-`command: ["python3", "/path/to/klammertext_ls.py"]` for the
-`text.klammertext` selector.  Everything in this package works the same
+`command: ["python3", "/path/to/klammertext_ls.py"]` (on Windows
+`"python"`) for the `text.klammertext` selector.  Everything in this package works the same
 with or without it.
 
 ## Troubleshooting