Add improveFreeNonzeros functionality

src/DistributeMat.c

src/FreeNonzeros.c

src/FreeNonzeros.h

src/Makefile

src/Options.c

src/Options.h

src/SparseMatrix.c

src/SparseMatrix.h

tests/Makefile

tests/Mondriaan.defaults

tests/runtest

tests/test_FreeNonzeros.c

tests/test_SparseMatrixFull2Symmetric.c

tools/Mondriaan.defaults