Add OCaml 4.08 support

[XVilka]

Also, since there is a long time error for OCaml 4.03 and OCaml 4.04 versions, maybe it makes sense to drop their support? After all they were released long time ago, 4.08 is out, and 4.09 will be ready quite soon as well...

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
+ /home/travis/.opam/opam-init/hooks/sandbox.sh "build" "dune" "subst" (CWD=/home/travis/.opam/ocaml-base-compiler.4.03.0/.opam-switch/build/asn1-combinators.0.2.0)
+ /home/travis/.opam/opam-init/hooks/sandbox.sh "build" "dune" "build" "-p" "asn1-combinators" "-j" "1" (CWD=/home/travis/.opam/ocaml-base-compiler.4.03.0/.opam-switch/build/asn1-combinators.0.2.0)
-       ocamlc src/.asn1_combinators.objs/byte/asn_combinators.{cmi,cmo,cmt} (exit 2)
- (cd _build/default && /home/travis/.opam/ocaml-base-compiler.4.03.0/bin/ocamlc.opt -w -40 -g -bin-annot -I src/.asn1_combinators.objs/byte -I src/.asn1_combinators.objs/public_cmi -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/bigarray-compat -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/cstruct -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/ptime -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/result -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/zarith -no-alias-deps -o src/.asn1_combinators.objs/byte/asn_combinators.cmo -c -impl src/asn_combinators.ml)
- File "src/asn_combinators.ml", line 94, characters 16-34:
- Error: Unbound value M2.max_binding_opt
[ERROR] The compilation of asn1-combinators failed at
        "/home/travis/.opam/opam-init/hooks/sandbox.sh build dune build -p
        asn1-combinators -j 1".
#=== ERROR while compiling asn1-combinators.0.2.0 =============================#
# context     2.0.3 | linux/x86_64 | ocaml-base-compiler.4.03.0 | pinned(file:///home/travis/build/mirleft/ocaml-asn1-combinators)
# path        ~/.opam/ocaml-base-compiler.4.03.0/.opam-switch/build/asn1-combinators.0.2.0
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p asn1-combinators -j 1
# exit-code   1
# env-file    ~/.opam/log/asn1-combinators-24700-ffb3fd.env
# output-file ~/.opam/log/asn1-combinators-24700-ffb3fd.out
### output ###
#       ocamlc src/.asn1_combinators.objs/byte/asn_combinators.{cmi,cmo,cmt} (exit 2)
# (cd _build/default && /home/travis/.opam/ocaml-base-compiler.4.03.0/bin/ocamlc.opt -w -40 -g -bin-annot -I src/.asn1_combinators.objs/byte -I src/.asn1_combinators.objs/public_cmi -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/bigarray-compat -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/cstruct -I /home/travis/.opam/ocaml-base-compiler.4.03.0/lib/ptime -I /home/travis/.opam/ocam[...]
# File "src/asn_combinators.ml", line 94, characters 16-34:
# Error: Unbound value M2.max_binding_opt

[XVilka]

Nevermind, not a portable solution across OCaml versions. What do you think about using stdlib-shims to help with this one?

[XVilka]

OK, should be fine after https://github.com/mirleft/ocaml-asn1-combinators/pull/27 is merged and https://github.com/mirleft/ocaml-asn1-combinators/issues/30 is fixed.

[hannesm]

thanks, this is supeerseeded by #31