Changes

• Add a log.log host export for the new graph-ts logging API (see the AssemblyScript API documentation for more information) (#599, #943).
• Measure the effect of tokio and database contention in subgraph indexing (#917, #918, #921, #926).
• Document the templates field in the manifest spec (#910, contribution by @dOrgJelli).
• Don't block chain head updates when there is back-pressure from block streams (#929).
• Write block ingestion and GraphQL query activity to Elasticsearch (#928).
• Add a database index for event sources in the event_meta_data (#945).
• Add database indexes for reference fields (#916, #944).
• Allow trace logging in production builds (#948).
• Bump tokio from 0.1.15 to 0.1.20 (#946).
• Increase thread pool size to 100 (#946).
• Make block stream errors non-fatal to allow to retry fetching blocks (#947).