rewrite the checkpointing code to dump 1 file per process instead of many files, use large offsets

[sebhtml]

[sebhtml]

format:

magicNumber (64 bits) format (32 bits) kmerLength (32 bits) numberOfMPIRanks (32 bits) sections (32 bits) <sectionKey><sectionOffset (64 bits)><bytes in container> <sectionKey><sectionOffset (64 bits)><bytes in container> <sectionKey><sectionOffset (64 bits)><bytes in container> <sectionKey><sectionOffset (64 bits)><bytes in container> <sectionKey><sectionOffset (64 bits)><bytes in container> <sectionContent> <sectionContent> <sectionContent> <sectionContent> <sectionContent>

sectionKey will be handles for checkpoints, in the source code, these will be associated to string names.

[sebhtml]

will need a Ray option to manage checkpoints

like:

Ray manage-checkpoints list checkpointDirectory -----> list checkpoints Ray manage-checkpoints remove checkpointDirectory checkpointName -----> remove a checkpoint