v0.19.0

• Add support for CLI plugins (e.g. graph indexer ...).
• graph init: Add contract name support.
• graph test: Speed up docker-compose down.
• graph test: Make docker-compose kill optional (depending on the system).
• Allow deriving from interface-typed fields.
• Allow specifying a graft base in the manifest.
• Fix Value is not a XYZ errors for null values.
• Fix path lookups in compiler script (thanks @fubhy!).
• Add support for yarn workspaces and otherwise hoisted node modules (thanks
  @fubhy!).
• Fix validating call handlers for functions with tuple parameters (#500).
• Properly unfold tuple event/call parameters in signatures.
• Pass --debug to AssemblyScript compiler.
• Dependency updates: acorn, fs-extra, yaml, docker-compose, gluegun, jest.