[opam-devel] license update

[Thomas Gazagnaire]

Hi,

I've updated the license of OPAM from GPL to LGPL+linking exception.

https://github.com/OCamlPro/opam/issues/612

The goal is to have more third-party libraries using the OPAM API directly, instead of calling the command-line, the first one of these being the automated test system for the OCaml plateform (https://github.com/ocamllabs/ocamlot).

Best,
Thomas