Add an HDF5 IParticleWriter, less verbose output (sometimes)

I'm adding an HDF5 writer for IParticles.

Right now I'm using it to write jets and the associated b-tagging information at half precision, mostly just a project to see how much space that can save without impacting our result. The outputs are structured as n_events x n_jets arrays, where n_jets is currently fixed at 6 and is zero padded for events under 6 jets, truncated for events with more.

The other change in this MR is that the output is set to WARNING by default in the unit test. This can be set back to INFO with the -v flag when running the test, or can be overridden with the FORCED_LOG_LEVEL environment variable. I'm setting the CI tests to INFO since people usually don't have to look at those outputs but having the log more verbose there is useful when you need to.

Closes #19 (closed)