Release 0.12.0

Added

• The template_dir option in the .changelogger.yml config file. This option
  allows users to override the default template location.
• Jinja templates now have full funcitonality, as the BaseLoader has been
  deprecated in favor of the FileSystemLoader.
• Exception information is now provided to help understand the cause of an
  upgrade exception.

Changed

• The jinja_rel_path versioned file key has been replaced with the template
  key.