111.28.00

- Added `Piecewise_linear.create_from_linear_combination`.

        val create_from_linear_combination : (t * float) list -> t Or_error.t

- Added `Time.is_{earlier,later} : Time.t -> than:Time.t -> bool`, which
  are easier to read than `Time.(<)` and friends.
- Added `Command.exec`, which allows one to include the `Command`
  hierarchy from one executable in another.

    `Command.exec` takes the file path to an executable that uses the
    `Command` module and returns a `Command.t` that integrates the
    executable (by exec'ing it), including providing recursive help and
    autocompletion as if it were a standard `Command.t`.

- Replaced most uses of `Hashtbl.replace` with `Hashtbl.set`.
- Renamed `Float.epsilon` to `robust_comparison_tolerance`, to avoid
  confusion with `epsilon_float`.