Triplet is initialized to nullptr when constructing a SparseMatrix.
Added addition for sparse matrices (with test).
Default argument for print.
Added addition of sparse matrices for rvalue references.
Updated the move constructor and move assignment operator.
Prevent copy assignment operations and created default constructor.
Merge branch 'master' of https://github.com/mortennobel/OOCholmod

Conflicts:
	src/sparse_matrix.h
	test/objects.h
	test/testsuite.cpp