Improve the Travis config

.travis.yml

@@ -1,29 +1,46 @@
 language: php
 
+sudo: false
+
+cache:
+    directories:
+        - $HOME/.composer/cache
+
 php:
     - 5.3
     - 5.4
     - 5.5
     - 5.6
     - hhvm
 
+matrix:
+    include:
+        - env: BUILD_TYPE=doc # marker environment variable to make the build matrix more readable in the UI
+          # Override the different steps of the build config
+          language: python
+          before_install: []
+          install: pip install Sphinx sphinx_rtd_theme
+          before_script: []
+          script: sphinx-build -nW -b html -d docs/build/doctrees docs docs/build/html
+          after_script: []
+
 env:
     global:
+        - BUILD_TYPE=code
         - secure: HhIy0kN0+UbuLeaVBk7O/utAYo038a9Emr8cdcfU+LQTu6CfGEbifH+LddXs6M/bSLTdNUSwQSnwycbeNYZ6iHCO/JI/vEgKxCTSecPerMXBIVCQjFZaCp3Tev8JJ40hKe78WJ/d0G4bGtIR6atR5V+H8Z29iwJeFtCj6doEt3o=
         - secure: oLadQTqg8HSEmUC0qEtChKd/R0ZiFNhzoZjIaa8kAJ0fjln/2xfNCBQIg4YstyjFy2kLiP6Lg8xW/RZljzyTHC+MCB9NNqTYjKLqFNRvFOlZUOnrAwc4sl4qjMYu9klWKa+rfyZzsuVWn++g829s2lFopkImqa6EB9DOR2TOT6w=
 
 addons:
     sauce_connect: true
 
+install:
+    - composer require satooshi/php-coveralls:dev-master --dev
+
 before_script:
-    - composer require satooshi/php-coveralls:dev-master --dev --prefer-source
-    - sudo easy_install -U Sphinx
-    - sudo pip install sphinx_rtd_theme
+    - mkdir -p build/logs
 
 script:
-    - mkdir -p build/logs
     - phpunit -v --coverage-clover build/logs/clover.xml
-    - sphinx-build -nW -b html -d docs/build/doctrees docs docs/build/html
 
 after_script:
     - php vendor/bin/coveralls -v