Travis: only test with opam 1.2
Sync changes
Use `Bytes` instead of `String` for mutable buffers.
Merge branch 'infidel-master' of github.com:avsm/ocaml-dns into infidel-master
Merge pull request #32 from avsm/infidel-master

0.12.0 changes
Switch to `Base64` v2, which uses `B64` as the toplevel module name.
Merge pull request #34 from avsm/master

Switch to `Base64` v2, which uses `B64` as the toplevel module name.