Add "composure" from "https://github.com/erichs/composure@1.3.1"

git-vendor-name: composure
git-vendor-dir: vendor/github.com/erichs/composure
git-vendor-repository: https://github.com/erichs/composure
git-vendor-ref: 1.3.1

vendor/github.com/erichs/composure/Makefile

@@ -0,0 +1,10 @@
+
+TARGET = tests
+all: $(TARGET)
+
+tests:
+	cd test && make tests
+
+clean::
+	rm -f test/*~ test/t/*~
+	rm -rf test/composure_test