Add code coverage

Author: tim

.travis.yml

@@ -4,4 +4,5 @@ python:
     - 3.5
 install:
     - pip install --process-dependency-links -e .[test]
-script: python -m pytest -v
+script: python -m pytest -v --cov tests
+after_success: codecov

codecov.yml

@@ -0,0 +1,26 @@
+codecov:
+  branch: master
+  bot: TimDaub
+
+coverage:
+  precision: 2
+  round: down
+  range: "70...100"
+
+  status:
+    project:
+      default:
+        target: auto
+        if_no_uploads: error
+
+    patch:
+      default:
+        target: "80%"
+        if_no_uploads: error
+
+  ignore:
+    - "tests/*"
+
+comment:
+  layout: "header, diff, changes, sunburst, uncovered"
+  behavior: default