Cusolver using Cholesky decomposition for symmetric matrices

Broadcasting tutorial

Change default of round() to be as NumPy and warn about it.

Add C code to RoundHalfToEven op.

by hardcoding the rounding instead of relying
on NumPy functions, so that this op should work
on CPU and on GPU.

Tests (CPU and GPU) passed on my computer, let's
see if jenkins/travis are ok with that.

Merged previous work implementing stack trace copy over and tests for…

(as I have changed the headers list).

Add a deprecation message to the old backend.

Initialize the blas kernels when creating the contexts.

Add user warning to prevent issue #5143

mixed

doc/tutorial/broadcasting.txt has been modified so it doesn't generate an error message during the documentation generation test.

doc/library/tensor/basic.txt contains a link to the tutorial page and links to the deleted section have been removed.

doc/glossary.txt does not contain anymore a link to a section that has been deleted and its linking to the broadcasting tutorial page.

doc/tutorial/broadcasting.txt contains the information about broadcasting and the info from doc/library/basic.txt is now there.

doc/sandbox/broadcasting.txt has been deleted as the tutorial page would contain the information about the broadcasting.

removed pruner function of EquilibriumOptimizer class