don't build the doc when pinning

use an environment variable BUILD_DOC=true to trigger ocamlbuild doc gen
Merge pull request #30 from dsheets/no-doc-pin

don't build the doc when pinning
Merge pull request #29 from avsm/master

Add sexp convertors for `Conduit_lwt_unix.ctx`
Merge pull request #32 from avsm/master

Continue the OCaml TLS merge
Merge branch 'master' of github.com:mirage/ocaml-conduit
Do not emit debug output when the `CONDUIT_DEBUG` variable is not set.
bump to 0.7.1