Document how to add scalar op and random number distribution.
Move the doc on how to make sparse ops and ops that wrap scipy in the extending module.
Fix link and better doc for scalar operation.
Add doc about OpenMP ops.
Fix doc link and add doc for numba.
small doc refactoring.
enable in travis-ci the apt cache.
Add a note about OpenMP Op doc.
Fix typos, some rephrasing.
Merge pull request #26 from lamblin/nouiz_doc_op

Fix typos, some rephrasing.
Merge pull request #1663 from nouiz/doc_op

Document how to add scalar op and random number distribution.