Folding algorithms extension

[okkevaneck]

• Algorithms don't need to return the pointer, folding algorithms can have rettype void.
• For deterministic algorithms, build load_tmp functions for loading intermediate results from a hash_fold()

[rubenhorn]

This would also be helpful in a similar way as #70 by implementing a check pointing mechanism:

• Register and optional signal handler (e.g., for SIGTERM, SIGINT, or both) with a checkpoint file path
• Upon receiving the signal, dump the intermediate result to the file
• When starting the algorithm with a checkpoint configuration, check for and load any existing intermediate result.