FIX parsing from non-original brainvision files
FIX unit_mul

Merge unit_mul with cal. Make unit_mul equal zero per convention.
FIX marker type

allow types other than Stimulus for trigger channel
ADD scale parameter

Add scaling parameter for non-native brainvision data. This allows for
the resultant data to be on the proper scale.
ENH provide scale factor, not just exponent

Change default from 0 to 1. accept float or int. make simple
multiplication instead of step for exponentiation.
Make unit_mul explicit
cosmit