Add Travis CI configuration

Travis CI is a hosted, continuous integration service.  Let's see how
it works out for us.

.travis.yml

@@ -0,0 +1,8 @@
+# Travis CI configuration
+language: c
+# Test with both gcc and clang:
+compiler:
+  - gcc
+  - clang
+# How to build:
+script: ./bootstrap && ./configure && make check