Add GitLab CI configuration

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>

.gitlab-ci.yml

@@ -0,0 +1,31 @@
+image: haskell:latest
+
+before_script:
+  - apt-get update && apt-get install xz-utils make
+  - export STACK_ROOT=`pwd`/.stack
+  - stack setup
+  - stack install --only-dependencies
+  - stack build
+
+build:
+  cache:
+    paths:
+      - _cache
+      - .stack
+  script:
+    - stack exec site build
+  except:
+    - master
+
+pages:
+  cache:
+    paths:
+      - _cache
+      - .stack
+  script:
+    - stack exec site build
+  artifacts:
+    paths:
+      - public
+  only:
+    - master