add spec tests

Makefile

@@ -0,0 +1,16 @@
+.POSIX:
+
+.PHONY: suite
+suite:
+	git submodule update --init modules/djot
+	for f in $$(find modules/djot/test -name '*.test' | xargs basename -a); do \
+		ln -fs ../../modules/djot/test/$$f tests/suite/$$f; \
+	done
+	(cd tests/suite && make)
+	cargo test --features suite
+
+clean:
+	cargo clean
+	git submodule deinit -f --all
+	rm -f tests/suite/*.test
+	(cd tests/suite && make clean)