Implemented ImageZigzagPersistence
* Changed ZigzagPersistence to support a visitor, and implemented
ImageZigzagPersistence
* examples/rips/rips-zigzag now computes using ImageZigzagPersistence
* PersistenceDiagram no longer records zero persistence pairs
* Added utilities/memory.h with report_memory() function
set (targets
cech-complex)
foreach (t ${targets})
add_executable (${t} ${t}.cpp)
target_link_libraries (${t} ${libraries})
endforeach (t ${targets})