Cross product and triple scalar product for all vectors (dense, tiny, engine)

[tkloczko]

First step : modification of type result for vector closure

Before that, the result type was enforced to be DenseVector< Array<T> >. So, neither TinyVector nor different Engine could have been handled.

The current modification aims at making the result type consistent with the input vector types of the closure.

Second step : extension of blas level1 for tiny vectors

This extension is made for:

• asum
• dot
• iamax
• nrm2
• raxpy
• rot
• rotm

Of course, in order to ensure good performance, it may be also necessary to add implementations for these functions into tinylevel1.

Last step : Add cross product and triple scalar product.

It consists in adding:

• OpCross struct
• copy and axpy closures to eval y=x1%x2 and y+=x1%x2 (temporary done by default)