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.

kpy/Makefile

@@ -1,8 +1,8 @@
 # kpy/ -- the Python binding of the Klammermachine.
 #
 # klammertext.cpp is a CPython extension module (see its header comment).
-# Like ref/reflect.so and sks/document/document.so it links against
-# libklammertext.so and shares the engine's class layouts, so it is rebuilt
+# Like ref/reflect$(DSO) and sks/document/document$(DSO) it links against
+# the shared library and shares the engine's class layouts, so it is rebuilt
 # whenever they are (mac/Makefile's "all" runs "make -C kpy"; com/Makefile's
 # "redo" and dev/rebuild.sh clean it -- a clean that misses a directory is a
 # mixed-object hazard, not a tidiness one).
@@ -19,7 +19,7 @@ K := $(KLAMMERTEXT_HOME)
 include $(K)/env/makefile.env
 
 LIBDIR := $(K)/lib
-LIBRARY := $(LIBDIR)/libklammertext.so
+LIBRARY := $(LIBDIR)/$(KLAMMERTEXT_LIBFILE)
 
 EXT_SUFFIX := $(shell $(PYTHON) -c 'import sysconfig; print(sysconfig.get_config_var("EXT_SUFFIX"))')
 MODULE := klammertext$(EXT_SUFFIX)
@@ -38,7 +38,7 @@ DEPFLAGS = -MMD -MP -MF $(@:.o=.d)
 # extension's dependencies from the extension's own directory, never from
 # PATH or an rpath -- there is none on PE); see makefile.env.
 ifneq (,$(filter MINGW% MSYS%,$(UNAME_S)))
-BESIDE_DLLS := libklammertext.so $(GCC_RUNTIME_DLLS)
+BESIDE_DLLS := $(KLAMMERTEXT_LIBFILE) $(GCC_RUNTIME_DLLS)
 else
 BESIDE_DLLS :=
 endif
@@ -54,14 +54,14 @@ $(MODULE) : $(OBJECTS) $(LIBRARY)
 		-o $@ $(OBJECTS) $(KLAMMERTEXT_LIB) $(LDLIBS)
 
 ifneq (,$(filter MINGW% MSYS%,$(UNAME_S)))
-libklammertext.so : $(LIBRARY)
+$(KLAMMERTEXT_LIBFILE) : $(LIBRARY)
 	cp $< $@
 %.dll : $(GCC_BIN)%.dll
 	cp $< $@
 endif
 
 clean :
-	rm -f $(OBJECTS) $(DEPFILES) klammertext.*.so klammertext.*.pyd libklammertext.so *.dll *~
+	rm -f $(OBJECTS) $(DEPFILES) klammertext.*.so klammertext.*.pyd *.dll *~
 	rm -rf __pycache__
 
 -include $(DEPFILES)