Switch code in lib subdir to ppx-style.
Inline some calls that js_of_ocaml was unable to recognise as tail-recursive
(cf. issue 14)
Minor update: documentation.
Added sexp_of_ support for GADTs, and remove the not-quite-working support
for of_sexp.
Improved the implementation of Exn.sexp_of_t, using the unique id in
exceptions in OCaml 4.02.
We use the identifier to map exception constructors to converters.
