GitLab

Pseudoinverse for polynomial matrix in bicgstab(l) to improve stability
(as in petsc);
Added RowMerger class for sum of sparse rows.

Synchronizing various changes

Replaced russian comments in doxygen.
Examples with OpenGL would not lead to error in cmake if no library is
found.

Petsc understands common parameters. Support for different option files
for Petsc and Trilinos. Please see files in examples/MatSolve.

Install instructions from readme file were tested on Linux machine.

Added code comments, small fixes and improvements.