Moved the DeformableSimplicialComplex class from simplicial_complex.h to DSC.h.
Added an abstract data structure API class called SimplicialComplex (in simplicial_complex.h) and its child the ISMesh class (in is_mesh_API).
Added functionality to the ISMesh class.
Updated the DeformableSimplicialComplex class such that it uses the ISMesh API instead of directly accessing the IS mesh.
Moved NULL simplex constants to the ISMesh class. Also get_edge and get_apices functions are moved to the ISMesh class.
Updated the split(tetrahedron) function.
Removed is_connected() function (replaced by get_edge).