Add Faust::prox_hankel and Faust::MatDense::adiagonal().

misc/test/CMakeLists.txt

src/faust_linear_operator/CPU/faust_MatDense.h

src/faust_linear_operator/CPU/faust_MatDense.hpp

src/faust_linear_operator/CPU/faust_prox.h

src/faust_linear_operator/CPU/faust_prox.hpp