If "_opam" is present in the tarball, append it to "opam"
List only code contributing authors.
Replace sub-dir opam/ with packages/ for OPAM 1.1.
Parse the OPAM packages for OPAM versions 1.0 and 1.1.

For OPAM 1.0, all opam files were in opam/ ; for OPAM 1.1, the whole
OPAM packages are stored hierarchically in packages/
Version 0.3.1