Calculator: add 'squared' and 'score'.

This is an attempt to add the requested "squared" operation without all
of the nasty trigger changes I introduced last time I tried.

Also added a constant for 'score' as both an attempt to better
understand that trigger regex and an historical oddity.

It's clear that if I want to continue with this I should make a lexer.
Merge pull request #498 from mwmiller/squared

Calculator: add 'squared' and 'score'.