0.37.0 Production Release

• Add size filter, which allows users to filter by resolution when available.
• Add aspect_ratio filter, which adds tall, wide, and square selectors. Only available in images where we know the dimensions.
• Add categories filter, which allows consumers to filter by illustration, photograph, or digitized_artwork.
• Expose license_url in search results.
• Fix incorrect link to PDM license.
• Throw a more detailed error message when users enter invalid query strings. Special thanks to @ritesh-pandey.
• Use boolean similarity to prevent description matches from dominating the search results. Special thanks to @Sando1.
• Fix broken tag filtering; see #253 and #394
• Instead of a 1-5 star rating for search relevance, switch to a boolean rating system.
• Use of unclosed quotation marks will not break the search results.
• Return the requested number of results, even after dead link filtering. Special thanks to @paulofilip3.
• Elasticsearch indexing can be distributed among an arbitrary number of EC2 worker nodes.
• oauth2 keys are verified by email.