release v1.9.0 (2015-09-06)

• Add support for PKCS12 (issue #17, thanks Baptiste Courtois).
• metadata: Add source_url and issues_url links.
• Documentation:
  • README: Add Real-world Examples section.
• Testing:
  • Run kitchen tests on CircleCI.
  • Travis CI: Use bundle cache.
  • Gemfile: Update RuboCop to 0.34.0.
  • Rakfile: Use Kitchen ruby class instead of sh.