v0.12.0

• Added support for responsive content images, which means that Timmy can now make images inserted in the post content via the WordPress Editor responsive.
• Optimized image markup by using the srcset attribute only if multiple images are available. If an image has only one image in srcset, it falls back to using the src attribute instead.
• Added src fallback attribute to all responsive images by default to fix invalid markup errors (as recommended by Picturefill).
• Optimized performance in the backend.
  • Only thumbnails and full sizes of images are shown in the backend to prevent on-the-fly resizing of images (e.g. in the Media Grid).
  • Uses full size instead of large size if 'large' is present as a size.
• Fixed selectable images sizes that appear in various positions in the backend.
• Added fallback for GIFs to return full size when image metadata can’t be read.
• Internal: Introduced new helper class for static helper functions.
• Internal: Replaced deprecated filter get_twig with timber/twig.