Testing new ways of packing block data from Vlasiator. Testapp in python & C for testing different variants. Tested by reading in double precision blocks from vlsv file, and comparing error metrics after compress/decompress cycle.

Planned variants:

1 Single precision (like now) 2 Single precision, scaling factor. 3 Half precision, scaling factor 4. ZFP https://github.com/LLNL/zfp 5. SZ https://github.com/disheng222/SZ

Scaling factors scale max value in block to max representable value of fp format. This is to use as much of the exponent bits as possible. Additionally, this value can be fine tune to preserve mass on a block level, which for lower precisions can be important.