Provides patch-level published-vulnerability verification for Bundler.

• Checks for vulnerable versions of gems in Gemfile.lock.
• Checks for insecure gem sources (http://).
• Allows ignoring certain advisories that have been manually worked around.
• Prints advisory information.
• Does not require a network connection.

Changes Accepted Upstream

• Add coverage analysis.
• Be clear in the README about allowed RubyGems versions.
• Broaden test suite a bit.
• Make tests more resilient to changes in details of the output from bundler-audit.
• Add tests for Database class.
• Clean up some lingering issues around the switch to requiring RubyGems 1.8.
• Reduce git noise for contributors.
• Add Ruby 2.0 to Travis test list.
• Whitespace cleanup.