#7: extracted propTense from entailments so it can be used in isSatisfiedProp as well
#7: added "john" and "amy" to the lexicon
so we can finally run all the "john eats" etc. examples
#7: tested perf entailments in case they are made impossible by a present tense prop
Closes #7.
Merge branch 'shlomo.7.entailments'