message: Add files= argument to Makefile builds
  You can now do "make test files=data/zeux.obj" instead of having to run
  meshoptimizer manually after make.
diff: MAKEFLAGS+=-r
  config=release
  +files=demo/bunny.obj
  BUILD=build/$(config)
  @@ -35,7 +36,7 @@ endif
  all: $(EXECUTABLE)
  test: $(EXECUTABLE)
  - $(EXECUTABLE) demo/bunny.obj
  + $(EXECUTABLE) $(files)
  format:
  clang-format -i $(SOURCES)
  