Replace Travis with Circle

We do lose some coverage here. Rather than confirming we build across a
slew of GHC versions, the sdist succeeds, etc, we just run the test
suite against the Stackage snapshot configured. Stackage snapshots is
the direction Haskell is moving, so I think this is an acceptable
simplification.

.travis.yml

@@ -1,41 +0,0 @@
-env:
- - CABALVER=1.18 GHCVER=7.6.3
- - CABALVER=1.18 GHCVER=7.8.4
- - CABALVER=1.22 GHCVER=7.10.1
- - CABALVER=head GHCVER=head
-
-matrix:
- allow_failures:
-  - env: CABALVER=head GHCVER=head
-
-install:
- - travis_retry sudo add-apt-repository -y ppa:hvr/ghc
- - travis_retry sudo apt-get update
- - travis_retry sudo apt-get install cabal-install-$CABALVER ghc-$GHCVER
- - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
- - cabal --version
- - echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
- - travis_retry cabal update
- - cabal install --only-dependencies --enable-tests --enable-benchmarks
-
-script:
- - cabal configure --enable-tests --enable-benchmarks -v2
- - cabal build
- - cabal test
- - cabal check
- - cabal sdist
- - export SRC_TGZ=$(cabal info . | awk '{print $2 ".tar.gz";exit}') ;
-   cd dist/;
-   if [ -f "$SRC_TGZ" ]; then
-      cabal install --force-reinstalls "$SRC_TGZ";
-   else
-      echo "expected '$SRC_TGZ' not found";
-      exit 1;
-   fi
-
-notifications:
-  email: false
-
-branches:
-  only:
-    - master

circle.yml

@@ -0,0 +1,14 @@
+dependencies:
+  cache_directories:
+    - "~/.stack"
+  pre:
+    - wget https://github.com/commercialhaskell/stack/releases/download/v0.1.6.0/stack-0.1.6.0-linux-x86_64.tar.gz -O /tmp/stack.tar.gz
+    - tar xvzOf /tmp/stack.tar.gz stack-0.1.6.0-linux-x86_64/stack > /tmp/stack
+    - chmod +x /tmp/stack && sudo mv /tmp/stack /usr/bin/stack
+  override:
+    - stack setup
+    - stack build
+
+test:
+  override:
+    - stack test