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.

mac/eval.cpp

@@ -320,7 +320,7 @@ std::string Eval::eval_command(katom_iter begin, katom_iter end)
         if (!khome.empty()) {
             lib_text = string_replace(lib_text, "*KLAMMERTEXT_HOME*", khome);
         }
-        fs::path libpath(lib_text + ".so");
+        fs::path libpath(lib_text + shared_library_suffix);
         // A relative library name not found from the cwd is searched in the
         // directories of the files the Machine has read (same rule as the
         // Python module path: the library lives next to the file using it).