datavault support for binary files

[fanmingyu212]

A binary file can reduce data file size and reduce the load/save time for data files. We can add an option in datavault to save binary files (default can be false to be backward compatible).

[gregllong]

I thought @aransfor is saving data files in .npy which I believe is numpy optimized binary file. @aransfor do you have some examples?

[aransfor]

I do this for the images other files don't seem to matter because they're so small

[fanmingyu212]

@aransfor @gregllong thanks for the information about the .npy file! Maybe we can implement the .npy format as a saving option for all datavault files? We have some data files saving photon timetags, and they can add up to tens of MB or more for an experiment.