fix missing name in doc "Of" -> "By"
adds an explanation code to the "apply design choise"
fix a turn of phrase
fix the missing apply name in the past "App.ly" -> "Ap.ply"
fix the reason that "App.ly" was rejected
add the naming in the past. "Apply._"
fix the explanation in "apply design choise - functor"
add how to support a substitute of functor in the apply design
remove the explation for langext 1.x