Ensure that all code lines are shorter than 72 characters

Makefile

@@ -1,6 +1,6 @@
 .PHONY: all base clean implode dist test force \
   docker-image docker-push-temporary-tag docker-print-temporary-tag \
-  docker-push-release-tag preview
+  docker-push-release-tag preview check-line-length
 
 SHELL=/bin/bash
 
@@ -276,3 +276,7 @@ implode: clean
 	rm -f $(MAKEABLES) $(ARCHIVES)
 	$(MAKE) -C examples implode
 	$(MAKE) -C libraries implode
+
+# This pseudo-target checks that the length of lines in the source files.
+check-line-length: $(INSTALLABLES)
+	! grep -En '^.{73,}$$' $^

docstrip.cfg

@@ -11,12 +11,12 @@
 -- permit persons to whom the Software is furnished to do so, subject to^^J%
 -- the following conditions:^^J%
 --^^J%
--- The above copyright notice and this permission notice shall be included^^J%
--- in all copies or substantial portions of the Software.^^J%
+-- The above copyright notice and this permission notice shall be^^J%
+-- included in all copies or substantial portions of the Software.^^J%
 --^^J%
 -- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,^^J%
 -- EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF^^J%
--- MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.^^J%
+-- MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND NONINFRINGEMENT.^^J%
 -- IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY^^J%
 -- CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,^^J%
 -- TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE^^J%