reviewed, updated, and merged uncertainty features by @howardcheung
uncertainty object now is in the uncertainty.py file, removed unneeded uncer_class.py
removed unneeded pint import from uncertainty.py
added uncertainty functions to the psychroom __init__ method.
added the uncertainty features to the io.read method. had to make a modification in order for it to preserve the ordering of the arguments to the uncertainty expression, not sure if this is entirely fixed.