API cleanup for binarywave (loadibw->load, move checksum to util, ...).

API cleanup for binarywave (loadibw->load, move checksum to util, ...).

Also moved byte_order to the util module and renamed a few functions
internal to the binarywave module so they start with an underscore.

The loadibw -> load (and saveibw -> save) change is because

  from igor.binarywave import load

gives you enough of an idea about what you're importing.  If you want
to keep it explicit in your client module, use

  from igor.binarywave import load as loadibw

which we do in the test.py module.