feedback on value-orientation

[wilbowma]

• [ ] why values-lang instead of expression-lang?
• [ ] aren't tail and value here exactly equivalent?
• [ ] "roughly equivalence"
• [ ] definitely something is wrong in this chapter with the treatment of "begin": the text is inconsistent with the grammar the text seems
• [ ] to be written as if effects don't include begin exprs
• [ ] (not specific to this chapter) is it values-lang or exprs-lang? seems inconsistent across chapters