[docu] Project file docu for PVCDBC.

.../c_PrimaryVariableConstraintDirichletBoundaryCondition.md

...raintDirichletBoundaryCondition/t_constraint_direction.md

...hletBoundaryCondition/t_constraint_threshold_parameter.md

...ConstraintDirichletBoundaryCondition/t_constraint_type.md

...riableConstraintDirichletBoundaryCondition/t_parameter.md

...n/PrimaryVariableConstraintDirichletBoundaryCondition.cpp

...ion/PrimaryVariableConstraintDirichletBoundaryCondition.h