Why the `nwb_`?

[choldgraf]

why are the core parts of file, utils, etc named as nwb_XXX? It seems unnecessary given that the main package is already called nwb, and in the examples when they're imported, they are already renamed w/ import nwb.nwb_utils as utils. Maybe this is a minor point but it'd be good to streamline the API to follow conventions of other major python projects in the numpy ecosystem