extensible terrain

[kostmo]

Closes #1641

The data/terrain.yaml file is now the authoritative source of terrains, though BlankT is still a hard-coded special case.

I have not changed the underlying integer representation of terrain in the world function, which means that the terrainIndexByName Map in the TerrainMap record is needed for translating between Int and TerrainType.

Demo

scripts/play.sh -i data/scenarios/Testing/1775-custom-terrain.yaml

Changes

• There used to be a function called integrateScenarioEntities that combined the EntityMap stored in the Scenario record with the global entity map. However, the global entity map is accessible at parse time of the Scenario, so we do the combining there and only ever store the combined map in the Scenario record.
• JSON Schema for terrain
• Removed the distinction between "World" attributes and "Terrain" attributes
• Unit tests for scenario-defined terrain and related validations
  • Validate existence of referenced terrain at scenario parse time
  • Validate attributes referenced by terrains at parse time

[byorgey]

Cool! Working through reviewing this slowly but surely.

[byorgey]

This is great! Many nice code improvements, and I like the added flexibility of custom terrain. It seems like this is also a good first step towards things like #742 and #205 .