Improved error handling in many places to detect missing files or NULL file handles.
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close() file before dying.
add the notebook
removed eigen3/viennacl includes from some class headers
Added subset stack in feature selection

Needed for keeping track of selected features which is required in a
classification scenario for unseen data.
update data-checkout to 24b8341
Merge pull request #2532 from lambday/develop

Added subset stack in feature selection
Added dummy main in variational approximation example

Fixes compilation error (reproduced with macosx 10.9 and its default compiler)
fixed #2536
Merge pull request #2537 from khalednasr/fix_rbm_notebook

fixed #2536
Fixed fallback main in examples in case of no eigen3 available
update the notebook
Attempt to fix QUICKSTART link in README
Fix broken links in README
Fixed various header Eigen3 guards in tests
Fixed python_static compilation error