Haxe externs for BitECS with macros sprinkled on top. Initial version of externs created using dts2hx, then cleaned up and improved upon.

Work in progress.

• Create a component from class definition.
• Reset/initialize components when adding them to an entity.
• Abstraction over query.
• Consider getting component stores from the query directly, instead of through the world?
• Add basic world-related bitECS API to World.
• Queries should be defined in Systems, but equal queries shouldn't be defined twice. That means we will need to generate some common storage type, probably in the World.
• Support for bitECS array types.
• Support for Not queries.
• Rethink macros.
  • Components – going from TypedExpr to Expr is too buggy.
  • More explicit approach for World and Systems, less typing?
  • Include the world in the queries, so we can just directly iterate them?