add command all to Makefile (qutip#236)

Makefile

@@ -12,10 +12,13 @@ format:
 test:
 	${JULIA} --project -e 'using Pkg; Pkg.resolve(); Pkg.test()'
 
+all: format test docs
+
 help:
 	@echo "The following make commands are available:"
 	@echo " - make docs: instantiate and build the documentation"
 	@echo " - make format: format codes with JuliaFormatter"
 	@echo " - make test: run the tests"
+	@echo " - make all: run every commands above"
 
-.PHONY: default docs format test help
+.PHONY: default docs format test all help