ENH add_dig_points, SetChannelMixin, reorganization

This is WIP.

Adds function apply_dig_points to apply hpi, cardinal, and dig points to the Info.

Remove unnecessary import functions for np.loadtxt.

Needs test. Not ready for review
right, by making it secret I just meant taking it out of the documentation. I think we could remove the option to save pickles though, originally we were thinking that we might be able to store additional information in pickles, but did we ever use that possibility?