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).
Deleted abstract SimplicialComplex class.

Maybe an abstract data structure API should be added at some time in
the future.
Renamed key types.

Renamed node_key_type, edge_key_type, face_key_type and
tetrahedron_key_type to node_key, edge_key, face_key and tet_key in the
ISMesh class.
Moved get_pos functions to ISMesh API.
Added is_interface functions to ISMesh API.
Moved set_pos and set_destination functions to ISMesh API.
Added is_boundary functions to ISMesh API.
Added get_destination function to ISMesh API.
Removed locked attribute from DSC class.
Added a get_label function in ISMesh API.
Moved update functions to ISMesh API.
Removed as many calls to the get() functions from the DSC class as possible.
Simplified the collapse functions.
Added a set_label function.