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/.travis.yml

@@ -0,0 +1,9 @@
+language: c
+script: make tests
+branches:
+  only:
+    - testing
+    - master
+before_install:
+ - sudo apt-get update -qq
+ - sudo apt-get install -qq ksh zsh