Images in plain text and the terminal; bounded build parallelism (from dev 16f82cc887af)

- @image under txt and ansi is a picture in characters, in five styles
  (Image_txt_style: halfblock the default, shade, ascii, quadrant,
  braille), sized to the terminal's width less a margin when ktext runs
  in one, every cell in its own colours under ansi; a figure's caption
  is centred under it and no txt caption is ruled off any more.
- The build compiles as many files at once as the machine has cores
  (JOBS; make -C com JOBS=1 for a small machine): the sub-makes' bare -j
  meant unlimited parallelism and exhausted 8 GB machines. The three
  install pages say "make -C com".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

doc/install/windows_source_install.md

@@ -138,13 +138,13 @@ sets `PYTHON=python`. Nothing is edited by hand.
 In the UCRT64 shell, in the repository:
 
 ```bash
-make -C com -j
+make -C com
 ```
 
-`-j` compiles in parallel; on a machine with 8 GB of memory or less the
-optimizing compiler may run out of memory and report `out of memory
-allocating`. If so, run `make -C com` without `-j`: slower, and it
-finishes.
+The build compiles as many files at once as the machine has cores. On a
+machine with 8 GB of memory or less the optimizing compiler may run out
+of memory and report `out of memory allocating`; if so, `make -C com
+JOBS=2`, or `JOBS=1`: slower, and it finishes.
 
 This builds the library (`klammertext.dll`), the Standard Klammer Set's
 components and the three commands (`ktext.exe`, `kdesc.exe`, `kdiag.exe`)
@@ -311,7 +311,7 @@ In the UCRT64 shell:
 ```bash
 cd $KLAMMERTEXT_HOME
 git pull
-make -C com -j
+make -C com
 ```
 
 
@@ -379,7 +379,7 @@ installed one may not. Install it from
 https://aka.ms/vs/17/release/vc_redist.x64.exe and try the import again.
 
 **"klammertext.dll was not found" or "libstdc++-6.dll was not found".**
-`bin\` is not on the `Path`, or the build did not finish: `make -C com -j`
+`bin\` is not on the `Path`, or the build did not finish: `make -C com`
 places the library and the runtime DLLs in `bin\` beside the commands.
 
 **"The shell Klammertext runs sh commands with on Windows is missing".**