Merge pull request #61 from j-b-m/master

print message when libexif is missing on configure
Add Brian, Janne, and Steinar to AUTHORS.
Transfer Ushodaya copyrights to Meltytech, LLC.

On September 30, 2014, Ushodaya Enterprises Limited assigned copyright
to Daniel Dennedy, acting on behalf of Meltytech, LLC.
Supplement avformat consumer YAML with info from wiki page.
Changes to YAML and metadata.rb to make ruby 1.9.3 happy.

The Ruby YAML parser does not like percent sign in double-quotes -
probably trying to expand it or something.
Fix resolving relative paths on Windows.
Add an option to not output the root attribute.