Adds travis CI integration.

.travis.yml

@@ -0,0 +1,36 @@
+# Use new container infrastructure to enable caching
+sudo: false
+
+# Choose a lightweight base image; we provide our own build tools.
+language: c
+
+# GHC depends on GMP. You can add other dependencies here as well.
+addons:
+  apt:
+    packages:
+    - libgmp-dev
+
+# The different configurations we want to test. You could also do things like
+# change flags or use --stack-yaml to point to a different file.
+env:
+- ARGS=""
+- ARGS="--resolver lts-2"
+- ARGS="--resolver lts-3"
+- ARGS="--resolver lts"
+- ARGS="--resolver nightly"
+
+before_install:
+# Download and unpack the stack executable
+- mkdir -p ~/.local/bin
+- export PATH=$HOME/.local/bin:$PATH
+- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
+
+# This line does all of the work: installs GHC if necessary, build the library,
+# executables, and test suites, and runs the test suites. --no-terminal works
+# around some quirks in Travis's terminal implementation.
+script: stack $ARGS --no-terminal --install-ghc install
+
+# Caching so the next build will be fast too.
+cache:
+  directories:
+  - $HOME/.stack