Merge branch 'multi_rhs' into 'master'

src/problem/Formulation.cpp

src/problem/Formulation.h

src/system/Solver.cpp

src/system/Solver.h

src/term/Assembler.cpp

src/term/Assembler.h

src/term/LinearTerm.cpp

src/term/LinearTerm.h

src/term/LinearTermInterface.cpp

src/term/LinearTermInterface.h