feat: Add variable name_suffix; Pass shellcheck; Discard useless variables from main script

Makefile

@@ -23,8 +23,10 @@ tests:
 	for test in $(tests_dir)/*.bats; do bats --verbose-run --print-output-on-failure "$$test"; done
 
 lint:
-	shellcheck $(src_dir)/boring-backup || true
-	shellcheck $(src_dir)/lib/* || true
+	shellcheck $(src_dir)/boring-backup
+	shellcheck $(src_dir)/lib/*.sh
+	shellcheck $(src_dir)/lib/handlers/sources/*.sh
+	shellcheck $(src_dir)/lib/handlers/targets/*.sh
 
 docs: builddir
 	# See rst2man(1), rst2html(1), https://docutils.sourceforge.io/docs/index.html