get rid of graph_tool, closes #43

ci/README.rst

 Continuous integration howto
 ============================
 
-DRAFT !!
-
-
-Docker reminder
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-Use docker_images/osname/Dockerfile to create a docker image :
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-For example::
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-    cd docker_images/debian
-    docker build -t fperignon/hysop
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-
-To start the image::
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-   docker run -ti fperignon/hysop bash
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-Images list::
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-   docker images
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-Then tag and push image on docker hub (might need login)::
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-     docker tag image_id fperignon/hysop:debian
-     docker push fperignon/hysop:debian
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-Pick image id in docker images list.
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-
-Gitlab-ci
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-To use a given docker image in job:
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-image: fperignon/hysop:debian
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-The image will be pulled from docker hub.
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-yml driver
-----------
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-See gitlab-ci documentation : http://docs.gitlab.com/ce/ci/yaml/README.html
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-In script, use -DCI_CONFIG=<something> option for cmake to send runner information to dashboard.
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+See scripts in utils to build, run, push and pull the docker image for continuous integration tests.