do not run the tests of dependencies, improve log outputs, etc

• Rename travis-opam into ci-opam (#101, @avsm)
• Do not run the tests of dependencies (#145, @edwintorok)
• Run depopts tests (#146, @edwintorok)
• Allow to use PACKAGE=name.version (#152, @samoht)
• Improve log outputs (folding, more debug message, etc
  (@Chris00, @edwintorok, @samoht)
• Automatically infer package name when using pkg.opam (#181, @samoht)