* add option numpy_version to build against the installed numpy version and not 1.15.0 (hardcoded version number), default is still 1.15.0
* add option skip_keras_test to skip keras test even if keras is installed (still enabled by default)
disable unnecessary warnings about ubuntu
* enable option PRIVATE for the compilation of the Python bindings (settings recommended on pybind11 documentation)
* test on debian 9
* Create a project for graph optimizer.
Move optimizer related code to the folder optimizer.
* Fix build failures.
* rebase and fix build failures.
* fix build failure.
* fix build failure with cuda path.
* fix python build failure.
* Move two transformers(memcpy and insert_cast) from framework to optimizer.
* rebase.
* SessionState should not depend on optimizer.
