make Trunc not depend on types/*
move basic files to Basics/*
fix pointer to Overture in configure.ac
remove no-longer-necessary Scheme hackery in Overture
appcontext is deprecated, use context instead; close #497
Merge pull request #499 from mikeshulman/appcontext

appcontext is deprecated, use context instead; close #497
Merge pull request #498 from mikeshulman/schemes

remove no-longer-necessary Scheme hackery in Overture