Prepare for comparison #2.
Implement basic heuristics for usage of element-wise constant parameters.
Progress on precalculated tables.
Progress on precalculated forms.
Check the DiscreteProblem for zero number of DOFs. fixes #85.
Add get_num_vertex_nodes, get_num_edge_nodes.
A fix in ComplexFilter.
Update of conditions for cache usage in assemble().
Shorten the names of elements in Mesh XML exports.
Save some xml sizes in Space, Solution.
Some XML optimizations.
Update of speed of XML save/load.
Update CMake.vars.example.
Add checks of mesh correctness right after load.
Delete the H2D_DISABLE_MULTIMESH_TESTS macro.

Last commits together: fixes #83.
CMake update.
BC documentation fix.
Move precalculated and constant forms to the new layer.
Remove unnecessary cmake messages.