Updated ocaml-react to latest version, 1.2.0. Changes include:
- Fix bug in dynamic creation of S.{diff,changes} (#8).
- Fix bug in dynamic creation of S.switch (#7).
- Add support for toplevel: automatically `open React` on `#require "react"`.
- Add `S.Bool.{flip,edge,fall,rise}`.
- Fix `S.switch` rank's initialisation.
- Add `E.l{1,2,3,4,5,6}`, lifting combinators on events.
- Add `E.Option.{some,value}`.
- Add `S.{Float,Int}.{zero,one,minus_one}`.
- Add `S.Bool.{zero,one}`.
- Add `S.Option.{none,some,value}`.
- Add `{S,E}.on` equivalent to `{S,E}.when_`.
- Deprecate `{S,E}.when_` (syntax error prone).
- Fix `S.bind`.
- Use package builder topkg for distribution.
- Add support for update steps, see the `React.Step` module. Allows to
  specify simultaneous primitive signal updates and event occurences.
  The functions returned by `{S,E}.create` now have an optional
  `?step` argument; if unused the previous semantics is preserved.
- Add support for strong stops, can be used on platforms where weak
  arrays are not to prevent leaks. The function `{E,S}.stop` now have
  an optional `?strong` argument; if unused the previous semantics is
  preserved.
- Change signature of `S.switch`. Any existing call `S.switch ~eq s es` can
  be replaced by `S.(switch ~eq (hold ~eq:( == ) s es))`.


(jaapb)