tests: Fuse-only tests are put in tools/tests/

tools/tests/fuse-three-files.should_get

+!LAUNCH: python ../../tools/fuse.py ../../data/results-two-clones.vidjil ../../data/results-two-clones.vidjil ../../data/results-two-clones.vidjil ; cat fused.vidjil
+
+$ Fuse the three files
+2: ListWindows: .1000, 1000, 1000.
+
+$ Check the producer string in output file
+1: "producer": "vidjil fuse"
+