Add build script for travis

Two issues with testing builds on travis:

1. Normal log output is too long and results in build getting cancelled
2. Quiet log output is too quiet and results in build getting cancelled

.travis.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+while :; do printf .; sleep 300; done & pid=$!
+trap "kill -TERM $pid" INT TERM EXIT
+make

.travis.yml

@@ -1,5 +1,5 @@
 language: cpp
 dist: trusty
 sudo: required
-script: make -s
+script: ./.travis.sh