When a numpy array was evaluated, it was interpreted as a list of
possible values (although we generaly want the parametre value to be the
array itself).

Also, we changed the way to identify to-be-evaluated strings. The now
must begin with "eval " and are expected to return an array.

read_array_description was renamed to evaluate_description and modified
to take info account the fact that configobj returns arrays and that the
parametre list may not be a numpy array.

This will be used to add some information to the configuration file.

Based on the same way the SED creation modules work.

PEP8 and other corrections.