Question scoring improvements and robustness for ask.py

Added a parabolic weighting function for the question scorer which aims to
prefer questions with a certain number of tokens and penalizes quadratically
based on the distance from the ideal number.
Also made error messages from ask.py write to stderr instead of stdout.
Merge branch 'master' of https://github.com/ercgn/11411-proj
Changed exception handling to print stack trace
Merge branch 'master' of https://github.com/ercgn/11411-proj