109.10.00

- Added `|>`, which means the same as `|!`, but is likely to replace
  it someday.  This is mostly because `|>` is an accepted notation
  elsewhere, particularly in F#.  In the future, we will consider
  eliminating `|!` in favor of `|>`, so as to avoid the duplication.
- Made `module Lazy` into a monad.
- Renamed
  `List.stable_dedup_involving_an_application_of_the_set_functor` as
  `List.stable_dedup_staged`.  Made it use `Staged.t` to make explicit
  the expectation of partial application.
- Added pretty printers for the toplevel to `Error` and `Info`.