Fixed NaN output into vtk files.

Added support for SuperLU (serial) solver.

Fixes for GCC.

Moved functionality to operate with dense matrices as INMOST service.

Added possibility to exchange data of type DATA_VARIABLE in parallel.

Added possibility to include external content in xml format.

Moved overloaded operators for variables from namespace INMOST into
global scope to prevent possible ambiguities in compilers.

Added perturbation algorithm for BCGS solver.