directly do an .extend() when evaluating stuff in _fallback_view
rename "contenttypes_supported" to "supported_contenttypes"
make up a proper "request.errors" response in "_fallback_view" to be more descriptive when failing on "Accept" or "Content-Type" header validation
minor enhancement: no "list"-ifying required when computing "predicate_product", better inline comments
refactor generator/evaluator for multiple predicates getting passed through to Pyramid 1:1