Version 0.15.8

New features:

• Rich output in zef.ui, via show, to_table and to_card.
• splice, alias zefops.
• Filegraphs and credentials are stored together in directory for ZefHub URL.
  This may require a new login with your credentials.
• Symbolic expressions.

Breaking changes:

• ZEFHUB_AUTH_KEY is repurposed for API keys for service jobs. API keys can be
  created for your account at console.zefhub.io.

Fixes:

• SimpleGQL graphs are kept alive by default.
• Fixes in ordering of graph delta commands.
• Zefops ZefGenerators internally now for reliable iteration.

Improvements:

• FlatGraphs:
  • FlatGraphs can absorbed other FlatGraphs from FlatRefs
• SimpleGQL:
  • Faster queries/updates with explicit IDs.
  • Queries work in consistent graph slice.
  • debug-level for extra info
• Core:
  • GraphSlices now hold a reference to their corresponding Graph.