Use C++ memory allocation

[paulo-vra]

Is your feature request related to a problem? Please describe.
I am trying to modify the code to support arbitrary precision by using a class in the definition of number_t instead of the basic C types. However, the class is not initialized when structures are allocated with malloc, calloc and realloc, resulting in crashes.

Describe the solution you'd like
Replace C memory allocation with C++ allocation, using new, delete and some STL containers.

Describe alternatives you've considered
Simply replacing malloc with new and free with delete doesn't work, some complex parts of the code (sffe.cpp) use realloc, and I couldn't replace it with std::vector.