Example dumping live session to disk in ingestable format #50

While rarely used, the previous package featured a way to dump all recorded device interactions to a binary file. It would be great to do this in the modern package. The idea is something like:

device = open_device(device_module, port=COM_PORT, raw_data_path="./my_data_dir")

If specified, all device interactions will be dumped to the folder specified above as a session.harp folder in a way that can be read back via data.open_dataset.

There are some edge cases related to what-to-do if the session.data folder already exists. Maybe we could either timestamp the folder or provide an overwrite flag that let's us overwrite the existing folder.

The example could do this on time-series data for one second, and then plot the result to a graph.