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.

sks/Makefile

@@ -1,31 +1,34 @@
 # Klammertext sks/ Makefile
-# Builds all .so files in sks/ subdirectories
+# Builds all the DSOs (document$(DSO): .so, on Windows .dll) in sks/
+# subdirectories
 
 K := $(KLAMMERTEXT_HOME)
 KS := $(K)/sks
 KM := $(K)/mac
 
-# Shared library that all .so files depend on
-LIBRARY := $(K)/lib/libklammertext.so
+include $(K)/env/makefile.env
+
+# Shared library that all the DSOs depend on
+LIBRARY := $(K)/lib/$(KLAMMERTEXT_LIBFILE)
 
 # Support directories (build .o files used by other sks/ components)
 SUPPORT_DIRS := kutil target
 
 # Excluded directories:
-#   kutil, target - support directories that build .o files, not .so
-#   book, phase - obsolete, not updated for libklammertext.so
+#   kutil, target - support directories that build .o files, not a DSO
+#   book, phase - obsolete, not updated for the shared library
 
-# Directories that build .so files (excluding support and obsolete directories)
-# Find all subdirectories with Makefiles that have .so build targets
-# (look for lines like "xyz.so :" or "all : xyz.so")
+# Directories that build a DSO (excluding support and obsolete directories):
+# every subdirectory whose Makefile names its product with makefile.env's
+# $(DSO) suffix ("document$(DSO) :", "all : document$(DSO)").
 SO_DIRS := $(shell for dir in $(KS)/*/; do \
-    if [ -f "$${dir}Makefile" ] && grep -qE '^[a-z]+\.so\s*:|all\s*:.*\.so' "$${dir}Makefile" 2>/dev/null; then \
+    if [ -f "$${dir}Makefile" ] && grep -qE '\$$\(DSO\)' "$${dir}Makefile" 2>/dev/null; then \
         basename "$$dir"; \
     fi; done | grep -v -E '^(kutil|target|book|phase)$$')
 
 .PHONY: all clean support $(SUPPORT_DIRS) $(SO_DIRS)
 
-# Default target: build support first, then all .so files
+# Default target: build support first, then every DSO
 all : support $(SO_DIRS)
 
 # Build support directories
@@ -37,7 +40,7 @@ kutil :
 target : kutil
 	$(MAKE) -j -C $(KS)/target
 
-# Pattern rule for .so directories
+# Pattern rule for the DSO directories
 # Each depends on the library and support directories
 $(SO_DIRS) : support $(LIBRARY)
 	$(MAKE) -j -C $(KS)/$@