GitLab

Replacing dereference of zero'th element by data();
Fixed issues in GridGen that prevented compilation by microsoft visual
studio compiler;
Fixed small bug introduced by previous commit.

Moving connections, markers, geometric type, sparse data from Storage
class to TagManager class by using standard handling of mesh data.

Added MPI_Allreduce wrapper with MPI_MAX operation.

Retrieval of elements by markers;
Introduced options for loading of files;
Fixed issues saving vtk format when not all topological tests are
active;
Introduced Connect / Disconnect functions for manipulations with mesh;
DrawGrid example can now visualize array of entered cells/faces for
debug purposes;
OldDrawGrid example demonstrates fast interactive mesh slicing and
onscreen element picking.

Initial test of doxygen documentation tool

some changes