Add doctest capability to the docs, run it in Travis CI

.travis.yml

@@ -6,5 +6,7 @@ python:
   - "pypy"
 install:
   - pip install -r dev_requirements.txt --use-mirrors
+  - python setup.py develop
 script:
   - python setup.py test
+  - make -C docs doctest

docs/index.rst

@@ -6,6 +6,11 @@
 Welcome to Elasticsearch's documentation!
 =========================================
 
+.. doctest::
+
+  >>> from elasticsearch import Elasticsearch
+  >>> es = Elasticsearch()
+
 Contents:
 
 .. toctree::