- base class with non-virtual destructor causes undefined behaviour
- missing return statements at the end of non-void functions
- missing const before char* function argument
- reordered initialization of class members
- misleading indentation after for statement
- fixed use of uninitialized variables
- fixed unsequenced modification and access to variables (the C++
  standard does not define the evaluation order of operands, so
  expressions with side-effects such as j++ cause undefined behaviour)

Removing parameter mesh from method getValue in operators.

Refactoring the Dirichlet and the Neumann boundary conditions.

Min. interations feature was fixed in the GMRES method.
Timers for explicit and semi-implicit timestepping were added.