pool_array no longer depend on allocation/deallocation order; unit test on pool_array; some fancy functions to retrive derivatives for variable/hessian_variable

Allows to compare results on meshes obtained from parallel runs with
different number of processors

Examples/AdaptiveMesh do not inherit Mesh anymore - easier to work with
the method

Examples/Fracture got the option to not to fill the space

SearchKDTree class to search for elements by coordinates in mesh (some
rearrangements and improvements may follow)

Code to support mesh adaptation in models

Fix boundary condition in TestSuite/cavity

algorithm for small elements elemenation via edge collapse

new comparator to sort elements by their measure

slice_func delete the other zone

Fix a bug requesting back/front cell of a face during mesh modification

Comment unfinished parts of inmost in AdaptiveMesh

Update elasticity example in Examples/ADMFD

Add algorithms to split faces and to glue faces of the mesh (for tests
with MFD elasticty)

Elasticity example in Examples/ADMFD/elasticity.cpp

Bug fix - when assigning a matrix with different storage container, the
number of rows and columns is changed after the assignment itself,
which leads to incorrect behavior of opeartor(i,j) of the matrix.

Fix compilation issue with std::isinf

Finish memory_pool implementation in container.h

Use of matrices allocated in memory pool for intermediate results in
dense linear algebra operations in inmost_dense.h

Use of memory pool for matrices in inmost_autodiff.h

Change error reporting and return type in Invert, Solve,
CholeskyInvert, CholeskySolve, PseudoInvert, PseudoSolve

Add unit tests for linear algebra on dense matrices.

cavity and backward facing step

introduced in previous commit

mpi.h included after stdio.h

fixes in ADMFD

Add Examples/ADVDIFF example for advection-diffusion

Add exotic grid generators to Examples/GridTools

Add Examples/TestSuits for tests of diffusion and advection-diffusion
problems

DrawGrid -> DrawGridTests