YAMP 1.2.3 (Final)

Some improvements on the way, like improved documentation, added
documentation tests, improved sign function (for complex numbers), added
helper, improved LU, QR and Choleksy decomposition, improved
QueryContext, added possibility for accessing the cholesky method and
fixed a bug in the assignment routine.
Updated portable project to 1.2.3 final (Feb 19)
Merge remote-tracking branch 'upstream/master'