use bench instead of benches dir for benchmarks

in order to be able to place benchmarks in separate crates, if placed in
benches, they will be automatically considered part of the main crate

separate crates are needed to

- share generated input crate,
- avoid adding unused dependencies to tests

Makefile

@@ -47,7 +47,7 @@ suite_bench:
 bench:
 	git submodule update --init modules/djot.js
 	for f in $$(find modules/djot.js/bench -name '*.dj' | xargs basename -a); do \
-		ln -fs ../modules/djot.js/bench/$$f benches/$$f; \
+		ln -fs ../modules/djot.js/bench/$$f bench/$$f; \
 	done
 
 cov: suite suite_bench
@@ -96,6 +96,6 @@ clean:
 	(cd tests/suite && make clean)
 	rm -f tests/bench/*.dj
 	(cd tests/bench && make clean)
-	rm -f benches/*.dj
+	rm -f bench/*.dj
 	rm -rf tests/afl/out
 	(cd examples/jotdown_wasm && make clean)